Peanut Butter Sheet Cake with Fluffy Chocolate Frosting
Rich peanut butter laced cake pieces with gooey peanut butter filling topped with fluffy chocolate buttercream frosting. This peanut butter sheet cake is for all the peanut butter and chocolate lovers!
Servings 24 servings
Calories 336kcal
Ingredients
Peanut Butter Sheet Cake
- 2 cups all purpose flour 298g
- 2 cups granulated sugar 396g
- ½ teaspoon baking soda
- ¼ teaspoon salt
- 1 cup water 250ml
- 1 ½ sticks unsalted butter 170g, divided
- ¼ cup canola oil 60ml
- 1 cup creamy peanut butter 250g, divided
- 2 eggs
- ½ cup buttermilk* 120ml
- 1 teaspoon pure vanilla extract
Fluffy Chocolate Buttercream Frosting
- 1 12-ounce bag chocolate chips
- 1 ¼ stick unsalted butter 176g
- 2 cup confectioners sugar 250g
- 1 teaspoon pure vanilla extract
- ¼ cup heavy cream 60ml
Instructions
Peanut Butter Sheet Cake
- Preheat the oven to 350°F and grease a 9x13 pan.
- In a large bowl or the bowl of a standing mixer, whisk together the flour, sugar, baking soda, and salt. In a small bowl, whisk the eggs, buttermilk and vanilla together, set aside.
- Bring the water and 1 ½ sticks unsalted butter to a simmer in a medium sized sauce pan. Stir in ½ cup peanut butter and oil. Stir until the peanut butter is completely incorporated then remove from the heat and add to the dry ingredients on low speed. Increase the mixer speed to medium as the wet ingredients mix.
- Slowly add the remaining wet ingredients to the batter and beat on medium-high speed for 1 minute, scraping down the sides of the bowl half way through. Pour the batter into the prepared 9x13 pan and bake for 33 to 36 minutes or until a toothpick inserted in the center of the cake comes out clean.
- Let the cake cool for 15 minutes, then evenly spaced poke holes ¾ of the way through the cake. I did 4 holes across the width of the cake and 6 holes down the length. (See notes for tools ideas to poke the holes.)
- Spread the remaining ½ cup peanut butter over the cake while the cake is warm but not hot. You need a little bit of warmth for the peanut butter to melt into the holes but you do not want it to melt into the cake. Let the cake cool completely before frosting with chocolate buttercream - this can be done in the refrigerator to speed up the process.
Fluffy Chocolate Buttercream Frosting
- While the cake is baking, melt 1 bag of chocolate chips in a double boiler* on the stove top. Let cool for 15 to 20 minutes. You want the chocolate to still be melted but not too warm so it will melt the butter in your buttercream.
- In a standing mixer or with a hand mixer, beat the 1 ¼ stick butter on high speed until pale and fluffy. Add the confectioners sugar and vanilla, slowly increase speed to medium-high as sugar incorporates.
- Repeat with the heavy cream. Once incorporated, increase speed to high and beat for 45 to 60 seconds until cream is fluffy like whipped cream - you will see the texture of the frosting change. Add the chocolate and increase speed to medium-high as ingredients incorporate, scraping down the sides of the bowl when needed.
- Using a spatula or frosting knife, spread the chocolate buttercream frosting over the cooled peanut butter sheet cake.
Notes
- For the best texture and results use a traditional smooth, creamy peanut butter where the oil does not separate. We like the JIF all natural peanut butter. Other fresh ground brands (e.g. Teddie's - which I love, just not for this cake) will leave a gritty texture and you may get oil separation during baking.
- If you do not have buttermilk, you can make it! Pour ½ cup milk into a bowl, remove 1 tablespoon of the milk and add 1 tablespoon of lemon juice. Stir and let it sit for 5 minutes.
- Some tools you can use to poke your cake - strawberry huller, the round end of a wooden spoon or spatula, the handle of a piece of flatware and just spin it in a circle, a piping tip, or a very wide straw.
- A double boiler system is easy to set up. Add 1 to 2 inches of water to a medium size sauce pan and set a heat proof bowl over the pan. The water should not touch the bottom of the bowl. Add the chocolate chips to the bowl and bring the water to a simmer. Stir until the chocolate is smooth and melty. This system prevents burning the chocolate.
Nutrition
Calories: 336kcal | Carbohydrates: 37g | Protein: 5g | Fat: 20g | Saturated Fat: 9g | Trans Fat: 1g | Cholesterol: 45mg | Sodium: 110mg | Potassium: 99mg | Fiber: 1g | Sugar: 28g | Vitamin A: 388IU | Vitamin C: 1mg | Calcium: 19mg | Iron: 1mg