Go Back
Stack of peanut butter marshmallow fudge brownies with bite taken out.

Peanut Butter Marshmallow Fudge Brownies

Yield: 24 Brownies (9X13-inch pan)
Prep Time: 2 hours 30 minutes
Cook Time: 30 minutes
Total Time: 3 hours

Ingredients

Brownies (or use your favorite brownie recipe):

  • ½ cup boiling water
  • 2 ounces (57 g) unsweetened chocolate, finely chopped
  • ⅓ cup (28 g) unsweetened or Dutch-process cocoa powder
  • 2 ⅓ cups (495 g) granulated sugar
  • ½ cup vegetable, canola, or other neutral-flavored oil (like avocado or grapeseed)
  • 4 tablespoons (57 g) salted butter, melted
  • 2 large eggs + 2 large egg yolks
  • 2 teaspoons vanilla extract
  • 1 ¾ cups (249 g) ounces all-purpose flour
  • ½ teaspoon salt

Peanut Butter Layer:

  • 1 ½ cups (383 g) crunchy or creamy peanut butter

Marshmallow Fudge Layer:

  • 10 large marshmallows or 1 1/4 cups mini marshmallows
  • 4 tablespoons (57 g) salted butter
  • ¼ cup milk, I use 2%
  • ¼ cup (21 g) unsweetened or Dutch-process cocoa powder (see note)
  • ¼ teaspoon salt
  • 1 ½ cups (171 g) powdered sugar

Instructions 

  • For the brownies: Preheat oven to 350 degrees F. Line a 9X13-inch metal pan with aluminum foil and lightly grease with cooking spray (the lining of the pan is optional but helps with cleanup).
  • In a large bowl, whisk together the boiling water and chopped chocolate until smooth (if the chocolate doesn't melt fully, microwave the water/chocolate mixture for 20-30 seconds). Add the cocoa powder and whisk together. Add the sugar, oil, butter, eggs and vanilla. Mix until smooth and well-combined.
  • Add the flour and salt and mix until just combined and no white streaks remain. Spread the batter evenly in the prepared pan. Bake for 25-30 minutes until crackly on top and set around the sides. Let cool for 10-15 minutes.
  • While the brownies are still warm, dollop the peanut butter across the top. Let it sit for a few minutes so the peanut butter softens (alternately, you can warm the peanut butter in the microwave) and spread into an even layer. Refrigerate until the peanut butter is set, about an hour.
  • For the marshmallow frosting: in a microwave-safe bowl (or in a saucepan over low heat on the stove), combine the marshmallows, butter, milk, cocoa powder, and salt. Heat for 1-minute intervals, stirring in between, until melted and smooth.
  • Add the powdered sugar a little at a time to the warm chocolate mixture and stir until smooth and well-combined. If the frosting starts to get a little clumpy, heat for 20-second intervals in the microwave (or over low heat on the stove) until it smooths out a little.
  • Spread the fudge frosting over the chilled peanut butter layer. Refrigerate until set, about an hour. Serve the brownies chilled or at room temp (they are also tasty frozen). To easily cut the bars, run a sharp knife under very hot water, wipe clean, and slice (running under hot water between cuts).

Notes

Brownie: you can substitute your favorite 9X13-inch brownie recipe for the base brownie layer if you'd like.
Cocoa: using Dutch-process cocoa in the frosting will yield a darker/richer frosting.