Let's Bake

Peanut Butter Sheet Cake

Yield Makes 20-24 slices 1x
Prep: 40 minutesCook: 40 minutesTotal: 1 hour 20 minutes

An easy Peanut Butter Cake topped with chocolate frosting and M&M’s.


Peanut butter cake

  • 230 grams (1 cup / 2 sticks) unsalted butter, room temperature
  • 180 grams (1 cup) brown sugar
  • 100 grams (1/2 cup) caster sugar or granulated sugar
  • 250 grams (1 cup) smooth peanut butter*
  • 1 teaspoon vanilla extract
  • 3 large eggs, room temperature
  • 2 teaspoons baking powder
  • 1/4 teaspoon salt 
  • 315 grams (2 and 1/4 cups) plain flour or all purpose flour
  • 240 ml (1 cup) full fat or whole milk

Chocolate frosting

  • 115 grams (1/2 cup or 1 stick) unsalted butter, room temperature
  • 150 grams (1 cup) good quality milk chocolate
  • 375 grams (3 cups) icing sugar or powdered sugar, sifted
  • 23 tablespoons full fat or whole milk
  • 1 tablespoon smooth peanut butter*
  • 180 grams (1 cup) mini M&M’s


  1. Peanut butter cake
    Preheat oven to 180 C (350 F) standard / 160 C (320 F) fan-forced. Grease and line a quarter sheet pan with baking or parchment paper.
  2. Place butter and sugars in a large mixing bowl. Beat together with an electric mixer on medium speed until pale and creamy. Add peanut butter and vanilla and mix together until smooth and combined.
  3. Next, add eggs, one at a time. Beat on a low speed to combine. Don’t worry if the mixture looks curdled – this is normal.
  4. Add baking powder, salt and half of the flour, followed by all of the milk. Beat on a low speed to combine, then add the final half of flour. The cake batter should be thick and smooth.
  5. Pour batter into prepare pan and bake for approximately 35-40 minutes or until cake is golden brown and a skewer inserted in the middle comes out clean. Leave in pan to cool completely.
  6. Chocolate buttercream
    To make the frosting, place butter in a large mixing bowl and beat with an electric mixer on medium speed for a couple of minutes until pale and creamy. Meanwhile melt the chocolate in a microwave, stirring in between 20 second bursts, until just melted and set aside to cool a little.
  7. Once the butter is very pale and creamy, add half the sugar and one tablespoon of milk and beat on low until the sugar is incorporated. Then, add the rest of the sugar and another tablespoon of milk, and again beat on slow until the sugar is incorporated before turning up to medium for another minute or so.
  8. Next, add melted chocolate to the buttercream, ensuring the chocolate is still smooth and melted but is not warm. Add peanut butter. Beat until the chocolate and peanut butter is completely mixed through. If the frosting is a bit thick, add an extra tablespoon of milk.
  9. Generously spread the chocolate frosting all over the cooled peanut butter cake. Scatter over mini M&M’s.


*Peanut butter: I recommend using a full fat processed peanut butter like Bega, Skippy and Jif for this cake, instead of a natural peanut butter.

Nutrition Information

Serving Size: 1 square Calories: 413 Sugar: 37.3 g Sodium: 100.5 mg Fat: 21.8 g Carbohydrates: 50.5 g Protein: 6 g Cholesterol: 57 mg
Nutrition information is a guide only.
Author: Jessica HolmesCategory: CakeCuisine: American
Recipe Card powered byTasty Recipes