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A single, perfectly cut square of a marshmallow peanut butter brownie on a clean surface, showcasing the fudgy texture and swirls.

Marshmallow Peanut Butter Brownies: The Ultimate Gooey Treat

The ultimate recipe for Marshmallow Peanut Butter Brownies! This guide delivers a perfectly fudgy and chewy brownie base, swirled with creamy peanut butter and topped with a gooey, toasted marshmallow layer.
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Prep Time 15 minutes
Cook Time 30 minutes
Total Time 45 minutes
Servings: 16 brownies
Course: Dessert
Cuisine: American
Calories: 250
Ingredients Equipment Method Notes

Ingredients
  

For the Brownie Batter
  • 1/2 cup unsalted butter melted
  • 1 cup granulated sugar
  • 1/4 cup packed light brown sugar
  • 2 large eggs room temperature
  • 1 teaspoon vanilla extract
  • 3/4 cup all-purpose flour
  • 1/2 cup unsweetened cocoa powder
  • 1/4 teaspoon salt
For the Swirl & Topping
  • 1 cup semi-sweet chocolate chips divided
  • 1/2 cup creamy peanut butter
  • 2 cups mini marshmallows

Equipment

  • 1 8x8 inch baking pan
  • 2 Mixing Bowls
  • 1 Whisk

Method
 

  1. Preheat your oven to 350°F (175°C). Grease and line an 8x8 inch baking pan with parchment paper, leaving an overhang to lift the brownies out later.
  2. In a large bowl, whisk together the melted butter, granulated sugar, and brown sugar until well combined. Beat in the eggs one at a time, followed by the vanilla extract.
  3. In a separate bowl, whisk together the flour, cocoa powder, and salt. Gradually add the dry ingredients to the wet ingredients and mix until just combined. Do not overmix. Fold in 1/2 cup of the semi-sweet chocolate chips.
  4. Pour the batter into the prepared pan. Warm the peanut butter in a microwave-safe bowl for 20-30 seconds until runny. Drop spoonfuls over the batter and use a knife to gently swirl it in.
  5. Bake for 20-25 minutes, until the brownies are mostly set but still soft in the center.
  6. Remove from the oven and immediately sprinkle the mini marshmallows and the remaining 1/2 cup of chocolate chips over the top.
  7. Return to the oven and bake for an additional 3-5 minutes, until the marshmallows are puffed and lightly golden. Watch carefully to prevent burning.
  8. Let the brownies cool completely in the pan on a wire rack before using the parchment paper overhang to lift them out and slice into 16 squares.

Notes

Do Not Overbake: For the fudgiest texture, err on the side of underbaking. A toothpick inserted should come out with moist crumbs, not clean.
Cooling is Crucial: Allowing the brownies to cool completely is essential for clean slices. Rushing this step will result in a gooey mess (though still a delicious one!).
Storage: Store in an airtight container at room temperature for up to 3 days for the best texture.