Chocolate Sheet Cake with Creamy Peanut Butter Frosting

Make Chocolate Sheet Cake with Creamy Peanut Butter Frosting for a crowd—rich chocolate sheet cake topped with silky peanut butter frosting.

Ingredients

• 1 cup (16 Tbsp; 226g) unsalted butter
• 1 cup (240ml) water
• 1/2 cup (41g) unsweetened natural cocoa powder (not dutch-process)
• 2 cups (250g) all-purpose flour (spooned & leveled)
• 1 teaspoon baking soda
• 1/4 teaspoon salt
• 2 large eggs, at room temperature
• 1 cup (200g) granulated sugar
• 1/2 cup (100g) packed light brown sugar
• 2 teaspoons pure vanilla extract
• 1/2 cup (120ml) buttermilk, at room temperature*
• 1 and 1/2 cups (405g) creamy peanut butter (do not use natural style)
• 1/2 cup (8 Tbsp; 113g) unsalted butter, softened to room temperature
• 3 cups (360g) confectioners' sugar
• 1/2 cup (120ml) heavy cream, half-and-half, or whole milk*
• 1 teaspoon pure vanilla extract
• pinch salt
• optional: 1/2 cup (135g) melted creamy peanut butter and 1 cup chopped peanut butter cups

Instructions

Step 1: Preheat and prepare the pan

Preheat the oven to 350°F (177°C) and generously grease a 12×17-inch half-sheet (jelly roll) pan so the batter will release easily after baking. Use a thin layer of butter or a neutral baking spray and consider a sheet of parchment for a tidy edge—this is the first practical step, setting you up to pour a very thin, even batter into a rectangular vessel.

Step 2: Melt the chocolate-butter base

In a small saucepan (or microwave-safe jug if you prefer), heat the unsalted butter, water, and natural cocoa powder together, whisking constantly until the butter has fully melted and the mixture is smooth and glossy. Remove from heat and let it stand briefly so the warm chocolate base stays fluid but not piping hot when it meets the dry ingredients.

Step 3: Whisk the dry ingredients

In a large, shallow mixing bowl whisk together the spooned-and-leveled all-purpose flour, baking soda, and salt until uniformly aerated and even in color and texture. This dry mix will be the backbone of the cake’s fine crumb.

Step 4: Combine the warm chocolate with the dry mix

Pour the warm chocolate-butter-cocoa mixture over the whisked flour mixture and slowly whisk until combined; the batter will be very thick at this point and have a deep matte chocolate sheen from the cocoa and butter.

Step 5: Blend the eggs and sugars, finish the batter

Whisk the room-temperature eggs with the granulated sugar and packed light brown sugar until cohesive, then stir in the vanilla. Pour this egg–sugar mixture into the chocolate batter and whisk until smooth, then whisk in the buttermilk until the batter loosens slightly and becomes homogenous. Scrape the thick, glossy batter into the prepared half-sheet pan, smoothing the surface with a spatula so the batter reaches the pan edges and forms an even rectangular layer.

Step 6: Bake and cool the sheet cake

Bake the sheet cake for 15–20 minutes (mine is often exactly 17); test with a toothpick for doneness—clean or with a few moist crumbs is perfect. Remove the pan to a wire rack and allow the cake to cool completely in the pan; chilling briefly in the refrigerator speeds this step if you have room for the large pan.

Step 7: Make the creamy peanut butter frosting

With a handheld mixer or stand mixer fitted with a whisk or paddle, beat the softened unsalted butter and creamy (non-natural) peanut butter on medium-high for about 2 minutes until utterly smooth and silky. Add confectioners’ sugar, the cream (or half-and-half), vanilla extract, and a pinch of salt. Start mixing slowly for 20 seconds, then raise speed and beat until the frosting is fluffy, light tan in color, and pipeable/spreadable; adjust thickness with more sugar or thin with more cream to reach a velvety, scoopable consistency.

Step 8: Frost, top, slice, and store

Spread the peanut butter frosting evenly over the completely cooled sheet cake using an offset spatula, leaving subtle swirl marks and small peaks that show the frosting’s creamy density. Scatter chopped peanut butter cups generously across the surface and finish with a glossy crisscross drizzle of caramel if you like. Slice into rectangles and serve; cover leftovers tightly and refrigerate for up to five days—the cake is delightful chilled.

Notes

• Use room-temperature eggs and buttermilk for a smoother, more homogenous batter.
• Chill the cake briefly if you need to speed up cooling before frosting.
• Use regular creamy peanut butter, not natural, for frosting stability.
• Test the cake early during baking to avoid overbaking; thin sheet cakes bake fast.
• Store covered in the refrigerator and bring slices to room temperature before serving.