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Fluffy Peanut Butter Sheet Cake

An incredibly moist and tender peanut butter cake baked in one pan and topped with a cloud-like, fluffy peanut butter frosting. The ultimate easy, crowd-pleasing dessert.
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Prep Time 20 minutes
Cook Time 30 minutes
Total Time 1 hour 20 minutes
Servings: 15 squares
Course: Dessert, Snack
Cuisine: American, Autumn
Calories: 580

Ingredients
  

For the Cake
  • 2 cups all-purpose flour
  • 2 cups granulated sugar
  • 1 tsp baking soda
  • 0.5 tsp salt fine
  • 1 cup water
  • 1 cup unsalted butter (2 sticks)
  • 0.5 cup creamy peanut butter not natural style
  • 0.5 cup whole milk
  • 2 large eggs room temperature
  • 1 tsp vanilla extract pure
For the Frosting
  • 0.5 cup unsalted butter softened (1 stick)
  • 1 cup creamy peanut butter
  • 1 tsp vanilla extract pure
  • 0.25 tsp salt fine
  • 4 cups powdered sugar sifted
  • 6-8 tbsp heavy cream or whole milk room temperature

Equipment

  • 9x13-inch baking pan
  • Medium Saucepan
  • Large mixing bowl
  • Electric mixer
  • Wire rack

Method
 

  1. Preheat oven to 350°F (175°C). Grease a 9x13-inch baking pan.
  2. In a large bowl, whisk together flour, sugar, baking soda, and salt. Set aside.
  3. In a saucepan, combine water, 1 cup butter, and 1/2 cup peanut butter. Heat over medium, stirring, until melted and simmering. Remove from heat.
  4. Pour the hot peanut butter mixture over the dry ingredients. Beat with a mixer on low until combined.
  5. Add milk, eggs, and vanilla to the batter. Beat on medium speed for 2-3 minutes until smooth.
  6. Pour batter into the prepared pan. Bake for 25-30 minutes, until a toothpick comes out clean. Cool completely in pan on a wire rack.
  7. For frosting, beat 1/2 cup softened butter and 1 cup peanut butter until creamy. Beat in vanilla and salt.
  8. On low speed, gradually add sifted powdered sugar until incorporated. The mix will be thick.
  9. Increase speed to medium. Beat in heavy cream, one tablespoon at a time, beating well after each. Beat for 2-3 minutes total until very light and fluffy.
  10. Spread the fluffy frosting over the completely cooled cake. Slice into squares and serve.

Notes

Use standard creamy peanut butter (like Jif or Skippy) for best texture. Cake must be completely cool before frosting. Store covered at room temperature.