06/13/2026
Peanut Butter Sheet Cake with Peanut Butter Frosting
Ingredients
For the Cake:
2 cups all-purpose flour
2 cups granulated sugar
1 teaspoon baking soda
1/2 teaspoon salt
1 cup (2 sticks) unsalted butter
1 cup water
1/2 cup creamy peanut butter
1/2 cup buttermilk (or substitute with regular milk + 1/2 tsp white vinegar)
2 large eggs, lightly beaten
1 teaspoon vanilla extract
For the Peanut Butter Frosting:
1/2 cup (1 stick) unsalted butter
1/2 cup creamy peanut butter
1/3 cup whole milk
3 1/2 cups powdered sugar, sifted
1 teaspoon vanilla extract
Instructions
Preheat and Prepare: Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking pan with butter or non-stick cooking spray.
Mix Dry Ingredients: In a large mixing bowl, whisk together the flour, granulated sugar, baking soda, and salt. Set aside.
Boil the Wet Ingredients: In a medium saucepan, combine the butter, water, and creamy peanut butter. Bring the mixture to a gentle boil over medium heat, stirring frequently until smooth.
Combine Wet and Dry: Pour the hot peanut butter mixture over the dry ingredients in your large bowl. Stir until just combined.
Add the Rest: Add the buttermilk, beaten eggs, and vanilla extract to the batter. Whisk until the batter is completely smooth and well blended.
Bake: Pour the batter into the prepared baking pan. Bake for 25–30 minutes, or until a toothpick inserted into the center comes out clean.
Start the Frosting: About 5 minutes before the cake is done baking, start the frosting. In a saucepan, combine the butter, peanut butter, and milk. Bring to a gentle boil over medium heat.
Whisk in Sugar: Remove the saucepan from the heat. Gradually whisk in the sifted powdered sugar and vanilla extract until the frosting is completely smooth and pourable (just like in the photo!).
Frost and Cool: Pour the warm frosting evenly over the warm cake immediately after taking it out of the oven. Use a spatula to gently guide it to the edges if needed. Let the cake cool completely in the pan so the frosting can set before slicing and serving.
