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Banana bars with peanut butter fudge frosting

A banana sheet cake with an easy peanut butter fudge frosting. Great for feeding a crowd!
0 from 0 votes
Prep Time 20 mins
Cook Time 30 mins
Cuisine American
Servings (click to change) 20
Author Helen

Equipment (affiliate links)


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)


  • Lightly butter a 9 x 13 inch cake pan / baking dish and preheat the oven to 175C / 350F (170C / 340F fan oven).
  • 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).
  • With the motor / whisk running, add the eggs one by one until combined, then whisk in the mashed banana, vanilla, and milk.
  • In a separate bowl, sift the flour together with the baking powder, baking soda, salt, and cinnamon.
  • 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.
  • 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.
  • Meanwhile, make the frosting. Combine the butter, milk, peanut butter and vanilla in a saucepan and heat and stir until melted together.
  • Slowly add the powdered / icing sugar until you have a smooth and thick frosting. Pour over the cake and spread evenly.
  • 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.


Don't have any buttermilk?

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).

Mixing the batter

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!

Cooking time

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

Decorating the cake

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!


Calories: 251kcalCarbohydrates: 48gProtein: 4gFat: 4gSaturated Fat: 1gCholesterol: 25mgSodium: 138mgPotassium: 142mgFiber: 1gSugar: 34gVitamin A: 50IUVitamin C: 1mgCalcium: 30mgIron: 1.1mg
Tried this recipe?Let me know if you liked it!