If you’re looking for a cake with main character energy, this key lime pie cake is IT! Featuring layers of soft key lime cake, silky key lime curd, buttery graham cracker clusters, and zesty key lime buttercream, it’s all of the iconic flavor profile of key lime pie in cake form. The textures going on in this cake make it SO delightful – you get the crunch of graham cracker clusters with the smooth key lime curd, moist and fluffy cake, and creamy buttercream. Every bite is truly out of this world and bursting with the distinct floral citrus flavor of key lime.
If you’re looking for a next-level cake recipe that’s still not *too* complicated, this one is perfect!
Why You’ll Love this Key Lime Pie Cake
- Bright, fresh citrus flavor. Nothing is artificial here. Fresh key limes are used to flavor the cake, curd, and buttercream. You can alternatively use bottled key lime juice or Persian limes if you can’t find fresh key limes.
- Tastes just like key lime pie. The flavor profile is spot on, but in irresistible layer cake form!
- Incredible texture. Every bite of this cake is incredible from the crunch of the graham cracker clusters paired with silky key lime curd, soft cake layers, and creamy key lime buttercream.
- Perfect summer cake. The bright, tropical flavor of key lime throughout makes this the ideal summer layer cake (but no one will complain if you make it any other time of year).
What Makes This a Key Lime Pie Cake
There are four different elements that make this key lime pie cake unbelievably good. The textures and key lime flavor make it so special:
- Key Lime Cake Layers. Ultra-soft cake layers flavored with key lime zest and juice. I used my favorite lemon layer cake as a starting point and the key lime version is just as soft, moist, and packed with fresh citrus flavor.
- Key Lime Curd. Each cake layer is filled with a generous amount of key lime curd that is so silky, sets up beautifully in the refrigerator, and adds zesty key lime flavor to every bite!
- Graham Cracker Clusters. Since traditional key lime pie has a graham cracker crust, this key lime pie cake has layers of buttery graham cracker clusters between the cake layers, and is used as garnish for the cake. This adds a beautiful crunch while matching that key lime pie flavor profile.
- Key Lime Buttercream. The key lime buttercream holds all of these layers together and adds the ideal creamy citrus element. It’s flavored with key lime zest and juice, both of which make it just the right amount of tart.
Key Limes vs. Persian Limes
The most common limes you’ll find in grocery stores is the persian lime. Key limes can be a little harder to find, but the difference is they’re smaller in size and the flavor profile is more intense and tart yet floral.
What if I Can’t Find Key Limes for this Recipe?
Key limes make the flavor of this cake so amazing, but they can be hard to come by at certain times of the year and locations. Fortunately, you can easily get bottled key lime juice on Amazon and may even be able to find it at your local grocery store. You can use an equal amount any time the recipe calls for key lime juice, and an equal amount of regular (Persian) lime zest any time the recipe calls for key lime zest.
If you’d rather use Persian limes for the entire cake, that’s fine too! The flavor profile will not be as distinctly floral and tart like key limes, but it will still have plenty of lime flavor. Do whatever makes the most sense to you!
How to Make a Key Lime Pie Cake
Before You Begin
- Separate the Eggs. The cake recipe uses 4 egg whites and the key lime curd recipe uses 4 egg yolks. I love that no part of the egg gets wasted here!
- Juice and Zest the Key Limes. If you’re using bottled key lime juice, skip this step. If you’re using fresh key limes, you’ll want to zest 2 key limes for the cake, 2 key limes for the curd, and then juice about 16 key limes to use between the cake and curd. You will need more zest and juice for the key lime buttercream, but I like to save that for when I’m ready to make that element.
Bake the Key Lime Cake Layers
Mix together the key lime cake batter and bake in three 6-inch pans (like you see pictured throughout this post) or two 8-inch cake pans. Cool the cake layers on a wire rack while you make the key lime curd.
Make the Key Lime Curd
Whisk together the key lime curd ingredients and set it over a pot of simmering water (make sure the bottom of the bowl doesn’t touch the water). Whisk continuously until the curd thickens and reaches at least 170ºF, then remove from the heat and whisk in the butter until melted.
Transfer the curd to a glass bowl or container, cover the top with plastic wrap, and refrigerate to thicken further. You can store it for up to 2 weeks.
Make the Graham Cracker Clusters
Combine roughly crushed graham crackers, melted butter, brown sugar, and salt. Spread the mixture into an even layer on a parchment-lined baking sheet and bake until golden (about 10 minutes at 325ºF). Cool completely.
When the graham cracker sheet is cooled, break it up into clusters. Store in an airtight container in the refrigerator until you’re ready to assemble the cake.
Make the Key Lime Buttercream
Zest one more key lime before juicing two more, then follow the instructions in the recipe card to make the key lime buttercream. If the cake and curd are cooled, you’re now ready to assemble the cake!
Assemble the Key Lime Pie Cake
Once the cake layers are cooled completely, level them to your desired height. Place the first layer on the turntable (glued to a cardboard cake round using a swipe of buttercream). Add a thin layer of key lime buttercream, then pipe a circle around the edge of the cake layer. Add another circle on top to create more height if you need to. Fill in the center with about ⅓ of the key lime curd and top with a layer of graham cracker clusters. Place the next cake layer on top and repeat the process of filling and stacking before adding the final layer on top, upside down so the bottom of the cake layer becomes the top of the cake.
For extra stability, I wrapped the entire cake in plastic wrap at this point and refrigerated for about 30 minutes to let the buttercream firm up. This prevents the cake layers from sliding around while trying to frost it.
Reserve a little over one cup of buttercream for the swirls on top, then use the rest of the buttercream to frost a smooth buttercream finish on the cake. Press some of the graham cracker clusters around the bottom third of the cake. Pipe swirls of key lime buttercream on the top of the cake (I used Wilton Tip 4B), place a halved key lime slice in between each swirl, and garnish with more graham cracker crumbles.
Tips for Success
- Make things ahead of time. To save you the stress of making and assembling this cake all in one day, make some of the elements ahead. You’ll find the full make-ahead guide in the notes of the recipe card below. I recommend baking the cake layers while making the key lime curd so you can use the egg yolks right away.
- Chill the curd before assembling. Make sure the key lime curd is fully chilled before filling the cake. Whisk it to make it silky again if needed.
- Use fresh zest. Don’t try to zest the key limes ahead of time because it will lose the natural oils needed for flavoring.
- Pipe a buttercream dam around the curd. To keep a soft filling like key lime curd contained between cake layers, it’s essential to pipe a buttercream dam around the edges of the cake layers. Do this by filling a piping bag with the key lime buttercream, snip off about ½ inch opening on the end, and pipe a circle about ¼ inch from the edge of the cake layer. Pipe another circle on top to create more height if needed.
- Refrigerate before frosting. When you’ve filled and stacked the cake, wrap it in plastic wrap and refrigerate it for at least 30 minutes to let the buttercream firm up before you frost it. This will create the extra stability needed to prevent the layers from shifting around while you add the final layer of frosting.
- Refrigerate after assembling, but serve at room temperature. Since this cake contains key lime curd, you’ll need to store it in the refrigerator. It tastes best at room temperature, so take it out of the refrigerator about 1-2 hours before serving.
Other Key Lime Cake Variations
Here are some other fun ways to adapt this key lime pie cake recipe to your needs:
- Key Lime Pie Cupcakes. Use a double batch of my lemon cupcake recipe as a base, but substitute the lemon zest and juice with key lime zest and juice. Fill each cupcake with key lime curd, top with key lime buttercream and graham cracker clusters. Boom, key lime pie cupcakes.
- Key Lime Sheet Cake. Make the key lime cake batter and bake it in a 9×13 metal baking pan at 325ºF for 30-35 minutes. Top with a layer of the key lime buttercream first, followed by the key lime curd and graham cracker crumbles. I’d save some of the buttercream to decorate the edges to make it extra pretty.
- Coconut Key Lime Cake. Replace the key lime cake layers with the coconut cake layers from this recipe. The coconut adds an even more tropical element!
- Gluten-Free Key Lime Pie Cake. Use 1:1 gluten-free baking flour in place of the cake flour in the recipe + gluten-free graham crackers to make this entire recipe gluten-free.
I hope you love this key lime pie cake as much as I do! My almost-six year old proclaimed it was the best cake I’ve ever made and he has had a LOT of my cakes. If you make it, let me know what you think in the comments below (don’t forget to rate the recipe!) and feel free to tag @sugarandsparrowco on Instagram if you post a photo.
Key Lime Pie Cake
Ingredients
- 1 1/4 Cups (300ml) whole milk, room temperature
- 1/4 Cup (60ml) fresh key lime juice* bottled or from about 6 key limes
- 2 1/2 Cups (265g) sifted cake flour* DIY recipe in notes
- 1 Tbsp baking powder
- 1/2 tsp salt
- 1 1/2 Cups (300g) granulated sugar
- 1 Tbsp grated lime zest from about 2 key limes or 1 Persian lime
- 1/2 Cup (113g) unsalted butter, room temperature
- 4 large egg whites, room temperature save the yolks for the key lime curd!
- 1/2 Cup (120ml) vegetable oil
- 1 tsp pure vanilla extract
Key Lime Curd
- 4 large egg yolks
- 2/3 Cup (133g) granulated sugar
- 1/3 Cup (80ml) fresh key lime juice bottled or from about 10 key limes
- 1 Tbsp grated lime zest from about 2 key limes or 1 Persian lime
- 1/4 tsp salt
- 5 Tbsp (71g) unsalted butter, cold and cut into Tbsp sized pieces
Graham Cracker Crumble
- 3/4 Cup (90g) graham crackers, roughly crushed about 6 full sheets
- 1/4 Cup (57g) unsalted butter, melted
- 2 Tbsp (25g) brown sugar light or dark
- 1/4 tsp salt
Key Lime Buttercream
- 1 1/2 Cups (339g) unsalted butter, room temperature
- 2 tsp lime zest from about 1 key lime or 1/2 Persian lime
- 5 Cups (600g) powdered sugar
- 1 Tbsp (15ml) fresh key lime juice bottled or from about 2 key limes
- 1/2 tsp pure vanilla extract
- 1 Tbsp whole milk, room temperature
- 1/4 tsp salt, or to taste
Garnish (Optional)
- 5 key lime slices, halved
Instructions
Make the Key Lime Cake Layers
- Preheat the oven to 350°F (177ºC). Grease and line three 6-inch or two 8-inch cake pans.
- Start by separating 4 large eggs, placing the egg whites in one bowl and yolks in another. Refrigerate the yolks in an airtight container* until you're ready to make the curd (I recommend making it while the cakes are baking). Set the egg whites aside.
- In a jar or measuring cup, combine the 1 1/4 Cups (300ml) of whole milk and 1/4 Cup (60ml) of key lime juice. Stir and set aside. It will curdle by the time you add it to the recipe at the end, and the curdling is the chemical reaction we want!
- Add the sifted cake flour, baking powder, and salt into a bowl and whisk to combine. Set aside.
- Using a stand mixer fitted with the paddle attachment, mix together the sugar and lime zest on low speed until fragrant and well combined, about 1 minute. Add the butter and cream it together with the lime-sugar mixture on medium speed until light and fluffy, 2-3 minutes.
- With the mixer on low, add the egg whites one at a time. Add the vegetable oil and vanilla extract, then turn the mixer to high speed and beat for one minute.
- Turn the mixer off and add the cake flour mixture all at once. Mix on low speed until just combined, then slowly pour in the key lime-milk mixture. Mix until smooth and fully combined, about 30 seconds.
- Pour the batter evenly between the prepared cake pans and bake for 28-32 minutes, until a toothpick inserted into the centers comes out clean or with a few moist crumbs. Cool for 5 minutes before removing the cakes from the pans. Transfer the cake layers to a wire rack to cool completely to room temperature.
Make the Key Lime Curd
- Fill a small saucepan with 2 inches of water and bring to a simmer, then turn the heat to medium-low to maintain the simmer.
- In a medium glass or metal bowl that fits well on top of the saucepan (without the bottom of the bowl touching the simmering water), whisk together the 4 large egg yolks, 2/3 Cup (133g) granulated sugar, 1/3 Cup (80ml) key lime juice, 1 Tbsp lime zest, and 1/4 tsp salt.
- Place the bowl on top of the simmering saucepan to create a double boiler and whisk the key lime mixture constantly, until it thickens, about 5-7 minutes. You'll know it's thick enough when it can coat the back of a spoon and the line holds when you run your finger through it. You can also use a thermometer to see that the mixture reaches 170ºF. At this point, remove the bowl from the heat and whisk in the cold butter until fully combined.
- Pour the key lime curd into a glass jar or container and cover the surface with plastic wrap to prevent a skin from forming while it cools. Place into the refrigerator to cool completely, about 1-2 hours. It will thicken and set as it cools.
Make the Graham Cracker Crumble
- Preheat the oven to 325ºF and line a baking sheet with parchment paper. Set aside. Add the 6 graham cracker sheets into a Ziploc bag and use a heavy rolling pin to roughly crush them into pieces, the largest pieces being no more than 1/4 inch in size.
- Pour the crushed graham crackers into a bowl and add the 1/4 Cup (57g) of melted butter, 2 Tbsp (25g) of brown sugar, and 1/4 tsp of salt. Mix together until fully combined, then spread onto the parchment-lined baking sheet.
- Bake for 8-10 minutes, until the graham cracker mixture is golden brown and fragrant, then remove from the oven and allow to cool completely to room temperature. Once cooled, break into pieces and store in an airtight container in the refrigerator until you're ready to assemble the cake.
Make the Key Lime Buttercream
- In a stand mixer fitted with the paddle attachment, combine the 1 1/2 Cups (339g) of butter and 2 teaspoons of lime zest. Beat together on high speed until creamy and light in color, about 5 minutes.
- Add the 5 Cups (600g) of powdered sugar a few cups at a time, mixing thoroughly on low speed after each addition and scraping down the bowl and paddle before adding more.
- Keeping the mixer on low speed, add the 1 Tbsp of key lime juice, 1 Tbsp of whole milk, 1/2 tsp of vanilla, and pinch of salt. Continue mixing on low until the buttercream is well incorporated and smooth, 1-2 minutes.
Assembly
- Once the key lime cake layers are completely cooled, level them to your desired height. Add a swipe of key lime buttercream onto a cardboard cake circle and place the first cake layer on top. Add a thin (1/4 inch) layer of key lime buttercream, then add about 1 cup of the buttercream into a piping bag and pipe a dam (circle) around the edge of the cake layer. Pipe a second circle on top to give the dam a little more height. Fill in the center with about 1/3 of the cooled key lime curd (it should reach about halfway to the top of the dam), then top with a layer of the graham cracker crumble until you reach the top of the dam. Place the second cake layer on top and repeat the filling and stacking process before placing the final cake layer on top, upside down so that the bottom of the cake layer becomes the top of the cake. Gently but tightly wrap the cake with plastic wrap and place it in the refrigerator for at least 30 minutes to let the buttercream dam set firm. Note that you'll have a little bit of key lime curd left over that you can either serve with the cake, use to decorate the top, or store for another dessert.
- To create the design pictured, reserve about 1 Cup of the key lime buttercream for the swirls on top, then use the rest to frost a smooth buttercream finish onto the chilled cake. Press some of the graham cracker crumble onto the bottom third of the cake while the frosting is still tacky. Place the rest of the buttercream into a piping bag fitted with Wilton Tip 4B and pipe swirls around the top edge, then place a halved key lime slice in between each swirl.
Notes
- The key lime cake layers can be made ahead and stored at room temperature, covered tightly in plastic wrap, for up to two days. Alternatively, you can cover with plastic wrap and store in the freezer for up to two months before thawing to room temperature.
- The key lime curd can be made ahead and stored in an airtight container for up to 2 weeks in the refrigerator, or in the freezer for up to 3 months.
- The graham cracker crumble can be made ahead and stored in an airtight container for up to 1 week in the refrigerator or 3 months in the freezer.
- The key lime buttercream can be made ahead and stored in an airtight container in the refrigerator for up to two weeks. When you’re ready to use it, bring it back to room temperature and re-whip in your stand mixer to bring back to smooth buttercream consistency.
- The assembled key lime pie cake can be made ahead and must be stored in the refrigerator. It will last 4-5 days refrigerated, but is freshest (and the graham crackers are crunchiest) closer to the assembly date. When you’re ready to serve, bring the cake back to room temperature by taking it out of the refrigerator 1-2 hours beforehand.
Leave a Reply