This chocolate peanut butter sheet cake pairs a moist cocoa cake with fluffy peanut butter frosting, a glossy chocolate drizzle, and chopped peanuts on top.
It bakes in a single 9×13 inch pan, so it easily feeds a crowd at birthdays, potlucks, and school events. The batter is whisked in one bowl, and the boiling water gives the chocolate a deep, rich flavor.
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Why This Chocolate Peanut Butter Sheet Cake Recipe Works
Boiling water poured into the batter blooms the cocoa, which intensifies the chocolate flavor and makes the cake very moist. The thin batter bakes into an even layer that is easy to frost.
The peanut butter frosting is whipped with butter and powdered sugar until light and fluffy, with a little salt to balance the sweetness. It spreads smoothly over a fully cooled cake.
A drizzle of chocolate glaze, chopped peanuts, and halved peanut butter cups add crunch and make the cake look finished with very little effort.
Ingredients for Chocolate Peanut Butter Sheet Cake
- 1 3/4 cups all-purpose flour (for the cake)
- 3/4 cup unsweetened cocoa powder (for the cake)
- 1 1/2 teaspoons baking powder (for the cake)
- 1 1/2 teaspoons baking soda (for the cake)
- 2 cups granulated sugar (for the cake)
- 1 teaspoon kosher salt (for the cake)
- 2 large eggs (for the cake)
- 1 cup milk (for the cake)
- 1/2 cup vegetable oil (for the cake)
- 2 teaspoons vanilla extract (for the cake)
- 2 teaspoons instant coffee powder, optional (for the cake)
- 1 cup boiling water (for the cake)
- 1 cup (2 sticks) unsalted butter, softened (for the frosting)
- 4 cups powdered sugar, sifted (for the frosting)
- 1/2 cup smooth peanut butter (for the frosting)
- 1/4 teaspoon kosher salt (for the frosting)
- 1 tablespoon milk (for the frosting)
- 1/2 cup semi-sweet chocolate chips (for the topping)
- 2 tablespoons heavy cream (for the topping)
- 3 tablespoons smooth peanut butter, warmed (for the topping)
- 4 ounces mini peanut butter cups, halved (for the topping)
- 1/4 cup salted peanuts, finely chopped (for the topping)
Cocoa powder: Unsweetened cocoa, sifted if lumpy, gives a deep chocolate flavor. Dutch processed or natural both work.
Boiling water: It blooms the cocoa and thins the batter, which is why the cake stays tender.
Instant coffee: A small spoonful deepens the chocolate flavor without a coffee taste, and it is optional.
Peanut butter: Use creamy, shelf stable peanut butter in the frosting so it whips smoothly.
Peanut butter cups: Halved miniature cups on top add chocolate and peanut butter in every bite.
How to Make Chocolate Peanut Butter Sheet Cake
1. Prep the pan Heat the oven to 350 degrees F. Grease a 9×13 inch metal pan with butter and line it with parchment paper, leaving an overhang on two sides.
2. Mix the dry ingredients Whisk the flour, cocoa, baking powder, baking soda, sugar, and salt in a large bowl until no lumps remain.
3. Add the wet ingredients Add the eggs, milk, oil, vanilla, and coffee powder. Whisk until the batter looks smooth and thick.
4. Add the boiling water Pour in the boiling water gradually while whisking. The batter will be thin, which is correct.
5. Bake the cake Pour the batter into the pan and bake 30 to 35 minutes, until a toothpick in the center comes out clean. Cool completely in the pan, about 1 hour.
6. Whip the frosting Beat the butter until fluffy, about 3 minutes. Add the powdered sugar a little at a time, then the peanut butter, salt, and milk, and beat until light.
7. Frost the cake Spread the frosting over the cooled cake with an offset spatula.
8. Add the toppings Melt the chocolate chips with the cream in the microwave in 20 second bursts. Drizzle over the frosting, then drizzle the warmed peanut butter. Top with the peanut butter cups and peanuts.
How to Serve Chocolate Peanut Butter Sheet Cake
Cut the cake into squares and serve at room temperature with cold milk or a scoop of vanilla ice cream. For a dessert table, pair it with red velvet brownies, gooey brownie pie, and coconut chocolate chip cookies. A slice also tastes great next to homemade strawberry cake for a colorful spread.
How to Store and Reheat Chocolate Peanut Butter Sheet Cake
Store the frosted cake covered at room temperature for up to 3 days. Refrigerate for up to 5 days if your kitchen is warm, and let slices sit out for 20 minutes before serving. To freeze, chill the cake until the frosting is firm, wrap it tightly in plastic wrap and foil, and freeze for up to 3 months. Thaw overnight in the refrigerator.
Tips and Variations for Chocolate Peanut Butter Sheet Cake
Use a metal pan. Metal pans bake the cake evenly. Glass pans may need a few extra minutes.
Cool completely. Frosting a warm cake makes the butter melt and slide off.
Sift the powdered sugar. Sifting keeps the frosting smooth and free of lumps.
Warm the peanut butter. A few seconds in the microwave makes the drizzle runny enough to pour.
Make it ahead. Bake the cake a day early, cover it, and frost it the day you serve it.
Cut clean slices. Use a hot, wiped knife for neat squares through the topping.
Change the toppings. Mini chocolate chips, crushed pretzels, or extra chopped peanuts work well.
Keep it safe. Refrigerate leftovers promptly, as explained in this UMN Extension guide to storing and reheating leftovers.
Frequently Asked Questions About Chocolate Peanut Butter Sheet Cake
How many people does a chocolate peanut butter sheet cake serve?
A 9×13 inch pan cuts into 20 generous squares or up to 24 smaller ones.
Can I make a chocolate peanut butter sheet cake without coffee?
Yes. The coffee is optional and only deepens the chocolate flavor. Leave it out and the cake will still taste rich.
Why is the batter for a chocolate peanut butter sheet cake so thin?
The boiling water makes the batter thin on purpose. That is what produces a moist, tender crumb.
Can I freeze the frosting?
Yes. Freeze it in an airtight container for up to 2 months, thaw it in the refrigerator, and beat it again before spreading.
Can I use natural peanut butter?
Creamy shelf stable peanut butter holds up better in frosting. Natural versions can separate and make it greasy.
Chocolate Peanut Butter Sheet Cake
Equipment
- 9×13 inch metal baking pan
- Parchment paper
- Large mixing bowl
- Whisk
- Electric mixer
- Offset spatula
Ingredients
Main Ingredients
- 1 ¾ cup all-purpose flour for the cake
- ¾ cup unsweetened cocoa powder for the cake
- 1 ½ tsp baking powder for the cake
- 1 ½ tsp baking soda for the cake
- 2 cup granulated sugar for the cake
- 1 tsp kosher salt for the cake
- 2 large eggs for the cake
- 1 cup milk for the cake
- ½ cup vegetable oil for the cake
- 2 tsp vanilla extract for the cake
- 2 tsp instant coffee powder optional, for the cake
- 1 cup boiling water for the cake
- 1 cup unsalted butter 2 sticks, softened, for the frosting
- 4 cup powdered sugar sifted, for the frosting
- ½ cup smooth peanut butter for the frosting
- ¼ tsp kosher salt for the frosting
- 1 tbsp milk for the frosting
- ½ cup semi-sweet chocolate chips for the topping
- 2 tbsp heavy cream for the topping
- 3 tbsp smooth peanut butter warmed, for the topping
- 4 oz mini peanut butter cups halved, for the topping
- ¼ cup salted peanuts finely chopped, for the topping
Instructions
Cooking
- Prep the pan. Heat the oven to 350 degrees F. Grease a 9×13 inch metal pan and line it with parchment paper with an overhang.
- Mix the batter. Whisk the flour, cocoa, baking powder, baking soda, sugar, and salt. Add the eggs, milk, oil, vanilla, and coffee powder, then whisk in the boiling water until smooth. The batter will be thin.
- Bake. Pour into the pan and bake 30 to 35 minutes until a toothpick in the center comes out clean. Cool completely, about 1 hour.
- Make the frosting. Beat the butter 3 minutes until fluffy, gradually beat in the powdered sugar, then add the peanut butter, salt, and milk until light and spreadable.
- Frost. Spread the frosting evenly over the cooled cake.
- Top. Melt the chocolate chips with the cream in 20 second bursts and drizzle over the cake, followed by the warmed peanut butter. Finish with the peanut butter cups and peanuts.
