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the best key lime pie layer cake recipe
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Key Lime Pie Cake

Layers of soft key lime cake, silky key lime curd, buttery graham cracker crumble, and zesty key lime buttercream – the iconic flavor profile of key lime pie in cake form!
Course Dessert
Cuisine American
Prep Time 55 minutes
Cook Time 50 minutes
Cooling Time 4 hours
Total Time 5 hours 45 minutes
Servings 15 slices

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

*DIY Cake Flour Recipe: if you can’t find cake flour locally, here’s how to make a homemade version using all purpose flour and cornstarch. Keep in mind that if you do use the homemade version, the gram measurement will weigh more (295g instead of 265g) since all-purpose flour is heavier than cake flour.  
*Key Limes: if you can't find fresh key limes locally, check your grocery store for bottled key lime juice or find it on Amazon. You can alternatively use Persian limes but the flavor won't be as distinctly key lime. 
*Storing Egg Yolks: if you need to store the egg yolks for longer than a few hours, cover them with cold water in an airtight container and place it in the refrigerator. They should last up to 4 days this way. When you're ready to use them in the curd, drain the water from the yolks before starting the recipe.
Make Ahead Tips:
  1. 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. 
  2. 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.
  3. 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. 
  4. 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. 
  5. 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.