Chocolate Sheet Cake

My favorite moist, decadent chocolate cake recipe that is so easy and quick to whip up, it'll become a forever go-to. Baked in a 9x13 pan and topped with a generous amount of fudgy chocolate frosting and rainbow sprinkles.

Course Dessert

Cuisine American

Prep Time 25

Cook Time 35

Cooling Time 2

Total Time 3

Servings slices

Equipment

9x13 baking pan

Ingredients

Chocolate Sheet Cake

2 Cups (265g) all purpose flour
1 2/3 Cups (340g) granulated sugar
2/3 Cup (60g) unsweetened natural cocoa powder Dutch-processed cocoa powder works too!
2 tsp baking soda
1 tsp baking powder
1/2 tsp kosher salt
1/2 Cup (120ml) vegetable oil
2 large eggs, room temperature
1 1/2 tsp pure vanilla extract
1 Cup (240ml) full-fat buttermilk*, room temperature DIY recipe in the notes
1 Cup (240ml) hot coffee or hot water

Chocolate Buttercream

1 1/2 Cups (339g) unsalted butter, room temperature
4 Cups (480g) powdered sugar
3/4 Cup (68g) natural unsweetened cocoa powder
4 Tbsp whole milk, room temperature
1 Tbsp pure vanilla extract
pinch of salt, or to taste

Garnish (Optional)

3 Tbsp rainbow sprinkles

Instructions

Make the Chocolate Sheet Cake

Preheat the oven to 325ºF and prepare a 9x13 metal pan or baking dish* by spraying the sides with baking spray and lining the bottom with parchment paper
Place all of the dry ingredients into the bowl of a stand mixer and stir on low for 30 seconds to fully combine them. Add the vegetable oil, eggs, vanilla, and buttermilk and mix on low until just combined. With the mixer still on low, add the hot coffee (or hot water) in a slow stream, then turn the mixer to medium and beat until smooth, about 2 minutes. The batter will be very thin.
Pour into the prepared pan and bake for 35-40 minutes, until a toothpick inserted comes out clean. Cool completely before frosting. You can either let it cool in the pan before decorating or remove it from the pan to decorate if you wish.

Make the Chocolate Buttercream

In a stand mixer fitted with a paddle attachment, whip the butter on medium-high speed until creamy and light in color, 4-5 minutes.
Scrape down the bowl and paddle, then add half of the powdered sugar and half of the cocoa powder. Cover the mixer with a clean kitchen towel (to prevent ingredients flying out of the bowl), then turn the mixer to low speed and mix until the ingredients start to come together.
Scrape down the bowl and paddle and add the rest of the powdered sugar and cocoa powder, and also the milk, salt, and vanilla extract. Cover the mixer with the kitchen towel once more and turn the mixer to low speed. Mix until the ingredients are combined.
Remove the kitchen towel, scrape down the bowl and paddle, then continue mixing on low speed until uniform and smooth, 2-3 minutes.

Assembly

Once the chocolate sheet cake is cooled completely, frost with the chocolate buttercream. To create the look pictured, use half of the chocolate buttercream to frost the cake surface with rustic texture. Add the remaining chocolate buttercream into a piping bag fitted with Wilton Tip 4B and pipe a shell border around the edges of the cake. Garnish with rainbow sprinkles.

Notes

*DIY Buttermilk recipe: add 1 Tbsp of white vinegar to a jar and top it with 1 Cup of whole milk. Stir and let sit for 15 minutes before using in the recipe.

*9x13 Baking Dish: I used a metal pan for this sheet cake, but a ceramic or glass baking dish will work just fine. You may need to add 10-15 minutes to the baking time since glass and ceramic materials take longer to heat.

Make Ahead Tips:

The chocolate sheet cake 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 chocolate buttercream can be made ahead and stored in an airtight container at room temperature for up to 1 day. Alternatively, you can store it 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 rewhip with your stand mixer to bring back to frosting consistency.
The frosted sheet cake can be stored at room temperature, covered with plastic wrap or aluminum foil, for up to five days.

To Make by Hand (Without a Mixer): In a large bowl, whisk the dry ingredients together until uniform. Add the vegetable oil, eggs, vanilla, and buttermilk, and whisk everything together until smooth. Whisking constantly, add the hot coffee (or water) in a slow, steady stream. Continue whisking until the batter is smooth and uniform. It will be very thin. Pour into prepared cake pans and bake according to the recipe above.