My peanut butter sheet cake is the ultimate easy dessert for peanut butter lovers. Using boxed cake mix with a few simple add-ins, I get a moist, tender cake bursting with peanut butter flavor, both in the cake and the creamy frosting. It’s family-friendly, kid-approved, and ready to feed a crowd in under an hour, which is perfect for busy parents like me!
Peanut Butter Sheet Cake with Cake Mix
I make my peanut butter cake with cake mix, so it’s foolproof even on busy weeknights! I melt creamy peanut butter into hot butter and oil for a smooth, decadent batter that’s easy to mix by hand–no electric mixer needed. Buttermilk adds a soft, tender crumb with just a hint of tang that makes this cake taste totally homemade. And the fluffy peanut butter frosting is a hit with my kids every time. For extra fun, try topping it with chopped peanut butter cups or peanuts for a bit of crunch!
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Avoid Scorching the Peanut Butter
Always remove the saucepan from heat before stirring in the peanut butter. I’ve learned the hard way that it scorches fast if you don’t! This small step keeps your batter smooth and silky, ensuring a perfectly moist peanut butter sheet cake every time.
Peanut Butter Sheet Cake Recipe
Equipment
- Kitchen Scale (optional)
- Baking Sheet (make sure it has a rim!)
- Hand Mixer
Ingredients
For the Cake
- 1 cup water
- ½ cup unsalted butter cut into large cubes (1 stick)
- 2 tablespoons vegetable oil
- ¾ cup creamy peanut butter
- 26.5 ounces yellow cake mix (2 (13.25-ounce boxes)
- ½ cup buttermilk room temperature
- 2 large eggs room temperature
- 2 teaspoons pure vanilla extract
For the Frosting
- 1½ cups unsalted butter slightly melted (3 sticks)
- 1½ cups creamy peanut butter
- 3 tablespoons heavy cream (35% fat)
- 1 tablespoon pure vanilla extract
- 5 cups powdered sugar
- peanut butter cups optional, for decoration
Instructions
- Preheat oven to 350°F. Line a 13×18-inch rimmed baking sheet with parchment paper (leave parchment paper slighter higher than the sides of the pan so it’s easier to lift the cake out after). Lightly spray parchment paper with nonstick spray then set aside.
- In a small saucepan set over medium heat, bring the water, unsalted butter, and vegetable oil to a boil. Remove from heat.1 cup water, ½ cup unsalted butter, 2 tablespoons vegetable oil
- Stir the creamy peanut butter into the saucepan until it’s melted and well combined with the rest of the butter mixture. Be sure that the saucepan is no longer over the stove heat for this step or the peanut butter will start to burn.¾ cup creamy peanut butter
- Pour this wet mixture into the cake mix and fold (by hand with a spatula; don’t use an electric mixer) until the wet ingredients are fully mixed with the dry ingredients. Let cool for 5 minutes before the next step.26.5 ounces yellow cake mix
- In a separate small bowl, whisk the buttermilk, eggs, and vanilla together.½ cup buttermilk, 2 large eggs, 2 teaspoons pure vanilla extract
- Pour the buttermilk mixture into the rest of the cake batter. Stir with a spatula until well combined.
- Pour the batter onto the prepared sheet cake pan and use a spatula to evenly distribute the cake batter in the pan.
- Bake in the preheated oven for 27-28 minutes, or until a toothpick inserted in the middle comes out clean.
- Remove cake from oven and let cool completely before frosting.
- While the cake cools, make the frosting: In a large bowl, using a hand mixer, beat the butter, peanut butter, heavy cream, and vanilla until smooth, about 1 minute. Beat in the powdered sugar slowly until fully mixed in, then beat on high until light and fluffy, about 5 minutes. If the frosting seems too thick, beat in an additional tablespoon of heavy cream.1½ cups unsalted butter, 1½ cups creamy peanut butter, 3 tablespoons heavy cream, 1 tablespoon pure vanilla extract, 5 cups powdered sugar
- Smooth an even layer of frosting over the top of the cake and decorate as desired.peanut butter cups
Notes
- I don’t recommend using natural peanut butter in this recipe. The oils will separate, resulting in a not very pleasant cake.
- For a bit more texture in your cake, you can use chunky peanut butter, or fold in chopped peanuts!
- You can make this cake with all different kinds of nut and seed butters, like almond butter, Nutella, cashew butter, or sunflower seed butter! Get creative!
- Remove the saucepan from the heat before adding the peanut butter to prevent scorching.
- To turn this recipe into a layer cake, you can simply cut out layers from the sheet cake pan, or pour the batter into 2 or 3 round cake pans. They can be 9-inch or 8-inch round pans, but be sure to only fill them about halfway. Bake for about 30-35 minutes.
- Nutritional information does not include optional decorations.
How to Make a Peanut Butter Sheet Cake Step-by-Step
Boil the Fats: Preheat your oven to 350°F, line a 13×18-inch rimmed baking sheet with parchment paper, lightly spray with nonstick spray, then set aside. In a small saucepan set over medium heat, bring 1 cup of water, ½ cup of cubed unsalted butter, and 2 tablespoons of vegetable oil to a boil. Once boiling, remove the pan from the heat.
Melt the Peanut Butter: Stir ¾ cup of creamy peanut butter into the saucepan until it’s melted and well combined with the rest of the butter mixture. Be sure that the saucepan is no longer over the stove heat for this step, or the peanut butter will start to burn.
Fold in the Cake Mix: Pour this wet mixture into 26.5 ounces (2 boxes) of yellow cake mix and fold (by hand with a spatula; don’t use an electric mixer) until the wet ingredients are fully mixed with the dry ingredients. Let cool for 5 minutes before the next step.
Mix the Buttermilk: In a separate small bowl, whisk ½ cup of room-temperature buttermilk, 2 large room-temperature eggs, and 2 teaspoons of vanilla extract together.
Thin the Batter: Pour the buttermilk mixture into the rest of the cake batter. Stir with a spatula until well combined.
Spread the Batter: Pour the batter onto the prepared sheet cake pan and use a spatula to evenly distribute the cake batter in the pan.
Bake the Cake: Bake in the preheated oven for 27-28 minutes, or until a toothpick inserted in the middle comes out clean. Remove the cake from the oven and let it cool completely before frosting.
Beat the Frosting: In a large bowl, using a hand mixer, beat 1½ cups of slightly melted unsalted butter, 1½ cups of creamy peanut butter, 3 tablespoons of heavy cream, and 1 tablespoon of vanilla until smooth, about 1 minute. Beat in 5 cups of powdered sugar slowly until fully mixed in, then beat on high until light and fluffy, about 5 minutes. If the frosting seems too thick, beat in an additional tablespoon of heavy cream.
Frost the Cake: Smooth an even layer of frosting over the top of the cake and decorate as desired. I topped mine with peanut butter cups.
How to Store
Store leftover peanut butter sheet cake in an airtight container at room temperature for up to 3 days, in the refrigerator for up to 5 days, or in the freezer for up to 3 months. Let thaw overnight in the refrigerator before enjoying at room temperature.
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