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Peanut Butter Sheet Cake with Dark Chocolate Frosting

If your favorite candy is a Reese's peanut butter cup, then this peanut butter sheet cake is just the thing you need! It's loaded with creamy peanut butter and topped with a dark chocolate cream cheese frosting that just takes it over the top. You're going to want to keep this recipe on hand all year long!
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Prep Time 45 minutes
Cook Time 35 minutes
Cooling and Frosting Time 1 hour
Total Time 2 hours 20 minutes
Servings: 16 slices
Course: Dessert
Cuisine: American
Ingredients Method Notes

Ingredients
  

For the Peanut Butter Cake
  • ¾ cup unsalted butter
  • ¼ cup canola oil (or other neutral-flavored oil)
  • ⅔ cup creamy peanut butter
  • ¾ cup brown sugar (packed)
  • ½ cup granulated sugar
  • 1 tsp baking powder
  • ¾ tsp baking soda
  • ½ tsp salt
  • 3 large eggs (room temperature)
  • 2 cups all-purpose flour
  • 1 cup buttermilk
For the Dark Chocolate Frosting
  • 8 oz cream cheese (room temperature)
  • ¼ cup unsalted butter (room temperature)
  • ½ cup unsweetened cocoa powder
  • 3 cups powdered sugar

Method
 

For the Peanut Butter Cake
  1. Preheat oven to 350°F. Line a 9x13 inch cake pan with parchment paper so that the edges are hanging over the long sides and then grease with butter or cooking spray (I like Pam for Baking).
  2. In a small saucepan over medium heat, stir the butter until it is melted. Remove the pan from the heat and whisk in peanut butter and oil until incorporated. Transfer the peanut butter mixture to a glass bowl or liquid measuring cup to cool.
  3. In the bowl of a stand mixer fitted with the paddle attachment, combine the sugars, baking powder, baking soda, salt, and eggs. Mix on low speed until moistened and then increase speed to high. Beat until thick, fluffy, and pale (about 7 minutes).
  4. Reduce the mixer speed to low and slowly pour in the peanut butter mixture. Mix until evenly incorporated. Add the flour and mix until just combined. Some streaks of flour will remain. Slowly beat in the buttermilk until just combined, do not overmix.
  5. Transfer batter to the prepared pan and evenly spread (batter will be thick and heavy).
  6. Bake until a toothpick inserted in the center comes out clean, about 30 - 35 minutes. Cool in pan before frosting.
For the Dark Chocolate Frosting
  1. In the bowl of a stand mixer fitted with the paddle attachment, beat the cream cheese and butter on medium speed until smooth (about 2 minutes). Scrape the bowl as needed.
  2. In a separate bowl, whisk together the cocoa and powdered sugar. With the mixer on low speed, slowly add the cocoa and powdered sugar mixture and mix until well blended. Increase speed to high and beat until fluffy and creamy.
  3. Frost the cake using a knife or offset spatula. Top with sprinkles if desired and enjoy!

Notes

  • Cake will last for 5 days stored in an airtight container in the refrigerator. Bring to room temperature before serving.
 
High Altitude Directions
  • Flour – increase by 2 tbsp
  • Baking Powder – decrease to 1/2 tsp
  • Baking Soda - decrease to 1/4 tsp 
  • Granulated Sugar – decrease by 1/2 tbsp 
  • Brown Sugar - decrease by 2 tsp
  • Eggs – use 4 instead of 3.
  • Increase oven temperature to 360° F
  • Decrease baking time by 5 or more minutes
 
 
Helpful Tools
Mixing Bowls | Sprinkles | Offset Spatula | Jif Creamy Peanut Butter |  Rodelle Cocoa Powder