Print

Peanut Butter Sheet Cake with Chocolate & Peanut Butter Frosting

A peanut butter sheet cake with a peanut butter & chocolate swirled frosting, topped with mini peanut butter cups.
Prep Time 30 minutes
Cook Time 20 minutes
Total Time 50 minutes
Servings 24 servings
Author Sam Merritt

Ingredients

Peanut Butter Sheet Cake

  • 2 cups flour (245 g)
  • 1 cup sugar (150 g)
  • 1 cup brown sugar packed (150 g)
  • ¾ tsp baking soda
  • ½ tsp salt
  • ¾ cup stick butter cut into Tablespoon-sized pieces (170g)
  • ¼ cup oil (60 ml)
  • 1 cup water (237 ml)
  • ½ cup creamy peanut butter (classic creamy, not natural) 145g
  • ½ cup buttermilk (118 ml)
  • 2 large eggs
  • 1 ½ teaspoons vanilla extract

Peanut Butter Frosting:

  • ½ cup creamy peanut butter (145 g)
  • 1/2 cup unsalted butter softened to room temperature (
  • 1 cup powdered sugar (130g)
  • ½ teaspoon vanilla extract
  • ½ teaspoon salt
  • 1 ½ Tablespoon heavy cream

Chocolate:

  • ½ cup semisweet chocolate chips (100g)
  • 1/2 cup unsalted butter softened (113g)
  • ½ tsp vanilla extract
  • 1 cup powdered sugar (130g)
  • 1 ½ Tablespoon heavy cream
  • 1/2 cup mini peanut butter cups halved

Instructions

Peanut Butter Sheet Cake

  • Adapted from Taste of Home
  • Preheat oven to 350F and grease a 15x10x1 jelly roll pan.  (I used this blue one)
  • In a medium-sized bowl, whisk together flour, sugars, baking soda, and salt.  Set aside.
  • In a medium-sized saucepan over medium heat, combine butter, water, and oil.
  • Stir occasionally until butter is completely melted and bring to a boil.  Immediately remove from heat and add peanut butter, stir until peanut butter is dissolved and mixture is smooth.
  • Gradually stir flour mixture into liquid mixture until completely combined.
  • Allow mixture to cool for 5-10 minutes.  Meanwhile, whisk together buttermilk, eggs, and vanilla in a separate medium-sized bowl.
  • Gradually stir buttermilk mixture into flour/peanut butter mixture, stirring until just combined.
  • Pour evenly into prepared jelly roll pan and bake on 350F for 18-22 minutes.
  • Remove from heat and allow to cool completely in pan.  Meanwhile, prepare your frosting.

Peanut Butter Frosting

  • Use an electric mixer to beat together butter and peanut butter until smooth.  Gradually add powdered sugar until combined. 
  • Stir in salt and vanilla.  
  • Gradually, with mixer on low speed, add heavy cream.
  • Increase speed to high and beat for one minute until well-combined (pause mid-way to scrape down the sides and bottom of the bowl).  
  • Scrape peanut butter frosting into a separate bowl, and then use the now-empty bowl to prepare your chocolate frosting.
  • In a microwave-safe bowl, microwave chocolate chips at 15 second intervals, stirring between intervals, until chips are completely melted. Set aside and allow to cool slightly.
  • In KitchenAid (or with electric hand mixer) cream butter.
  • Add sugar gradually until well-combined (scrape down bottom and sides of bowl as needed).
  • Stir the chocolate (it should be melted but should not be too hot) and add it to your butter/sugar mixture.
  • Beat on medium-speed until well-combined.
  • Gradually, with mixer on low speed, add heavy cream.
  • Increase speed to high and beat for one minute until well-combined (pause mid-way to scrape down the sides and bottom of the bowl).  
  • Drop frosting by spoonful, alternating chocolate and peanut butter, over sheet cake.
  • Use a spatula to spread and swirl frosting.
  • Sprinkle with halved mini Reese's cups.
  • Cut and serve.