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Peanut butter sheet cake, cut into squares.

High Altitude Peanut Butter Sheet Cake

Heather Smoke
An easy-to-make peanut butter sheet cake that's a cross between a cake and a cookie bar, with fudge like peanut butter icing.

All recipes on Curly Girl Kitchen are developed for high altitude at 5,280 feet. See FAQs for adjusting to higher or lower elevations.

5 from 1 vote
Prep Time 15 minutes
Cook Time 35 minutes
Total Time 50 minutes
Course Dessert
Cuisine American
Servings16

Equipment

  • 8 or 9 inch baking pan

Ingredients
 

Cake

  • ½ cup unsalted butter
  • cup creamy peanut butter
  • ¼ cup whole milk
  • cup granulated sugar
  • cup light brown sugar, lightly packed
  • 2 large eggs
  • 2 tsp vanilla extract
  • 2 cups + 2 tbsp all-purpose flour, fluffed, spooned and leveled
  • 1 ½ tsp baking powder
  • ½ tsp coarse Kosher salt (if using table salt, use half the amount)

Frosting

  • ½ cup unsalted butter
  • ¼ cup creamy peanut butter
  • 1 cup powdered sugar
  • ½ tsp vanilla extract
  • tsp coarse Kosher salt
  • flaky finishing salt (if using table salt, use half the amount)

Instructions
 

Cake

  • Preheat the oven to 350 F, and position a rack in the center of the oven. Lightly spray an 8 or 9 inch square baking pan with non-stick baking spray, or line with parchment paper.
  • In a saucepan over medium heat, melt the butter. Add the peanut butter and milk, and stir until smooth. Remove from the heat.
  • In a bowl, whisk together the warm peanut butter mixture with the granulated sugar and light brown sugar. Whisk in the eggs and vanilla.
  • Separately, combine the flour with the baking powder and salt. Add the dry ingredients to the wet ingredients and stir together just until combined. The batter will be thick.
  • Spread the batter into the prepared pan, and bake for about 30-35 minutes (for an 8 inch pan) or 25-30 minutes (for a 9 inch pan), until a toothpick or cake tester inserted in the center comes out clean, or with moist crumbs clinging to it.
  • Let the cake cool in the pan for 1 hour, then add the icing while the cake is warm.

Icing

  • In a saucepan over medium heat, melt the butter. Stir in the peanut butter until smooth. Stir in the powdered sugar, vanilla and salt. Stirring constantly with a rubber spatula, bring the frosting to a simmer, and remove from the heat when it begins to bubble.
  • Immediately, pour the frosting over the cake. Let sit for several hours, until the frosting is firm and set. Sprinkle the top with flaky finishing salt, then cut into squares.
Keyword High Altitude, Peanut Butter, Sheet Cake
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