Banana sheet cake with peanut butter fudge frosting

A banana sheet cake with an easy peanut butter fudge frosting. Great for feeding a crowd!
Course Dessert
Prep Time 20 minutes
Cook Time 30 minutes
Total Time 50 minutes
Servings 20
Calories 251 kcal
Author Helen


For the sheet cake

  • 1 1/2 sticks of butter
  • 1 cup sugar
  • 1/2 cup brown sugar
  • 3 eggs
  • 1 cup mashed ripe banana 2-3 bananas, depending on size
  • 1 1/2 teaspoons vanilla essence
  • 1 1/2 tablespoons buttermilk or sour milk (see note below)
  • 2 1/2 cups plain flour
  • 1 teaspoon baking powder
  • 1/2 teaspoon baking soda
  • 1/2 teaspoon salt
  • 1/2 teaspoon ground cinnamon

For the peanut butter fudge topping

  • 3/4 stick of butter
  • 4 tablespoons milk
  • 1/3 cup peanut butter
  • 2 teaspoons vanilla essence
  • 2 1/2 cups powdered / icing sugar powdered / icing sugar
  • 6 peanut butter cups chopped into pieces (optional)
US Customary - Metric


  1. Lightly butter a 9 x 13 inch cake pan / baking dish and preheat the oven to 175C / 350F (170C / 340F fan oven).
  2. In a food mixer or food processor (or in a bowl with a hand-held electric whisk), soften the butter (about a minute), then add the sugars and cream together until light and fluffy (about 2 minutes).
  3. With the motor / whisk running, add the eggs one by one until combined, then whisk in the mashed banana, vanilla, and milk.
  4. In a separate bowl, sift the flour together with the baking powder, baking soda, salt, and cinnamon.
  5. Slowly add the flour mixture to the wet ingredients (pour wet mixture into a bowl if you’ve used a food processor), mixing until just combined.
  6. Pour the batter into the cake pan / baking dish and bake for 30 minutes or until a skewer inserted into the centre of the cake comes out pretty clean. Leave to cool in the pan.
  7. Meanwhile, make the frosting. Combine the butter, milk, peanut butter and vanilla in a saucepan and heat and stir until melted together.
  8. Slowly add the powdered / icing sugar until you have a smooth and thick frosting. Pour over the cake and spread evenly.
  9. Sprinkle over the chopped peanut butter cups (if using). Pop the whole pan in the fridge or freezer for a short while to set the frosting a bit, then slice and serve.

Recipe Notes

If you don’t have any buttermilk and don’t want to buy any just for this recipe, simply add about ¾ tablespoon vinegar or lemon juice to ordinary milk and let stand for 5 minutes (I always do it this way, as buttermilk isn’t a standard ingredient here in the UK).

Don't overmix after you add the dry ingredients to the wet. Just mix the flour in until just combined. A bit lumpy is fine!

Begin checking the cake after 25 minutes as cooking time will vary a little depending on your oven.

Feel free to use Reese’s Pieces or Peanut Butter M&Ms instead of Peanut Butter Cups for decoration - or just skip this final step altogether!

Nutrition Facts
Banana sheet cake with peanut butter fudge frosting
Amount Per Serving
Calories 251 Calories from Fat 36
% Daily Value*
Total Fat 4g 6%
Saturated Fat 1g 5%
Cholesterol 25mg 8%
Sodium 138mg 6%
Potassium 142mg 4%
Total Carbohydrates 48g 16%
Dietary Fiber 1g 4%
Sugars 34g
Protein 4g 8%
Vitamin A 1%
Vitamin C 1.2%
Calcium 3%
Iron 5.9%
* Percent Daily Values are based on a 2000 calorie diet.