These Peanut Butter Marshmallow Brownies are what happens when a classic fudgy brownie collides with gooey marshmallows and creamy peanut butter. You get a rich chocolate base, pockets of melted marshmallow, and ribbons of peanut butter swirled over the top.
Every bite is a mix of chewy edges, soft centers, toasted marshmallow, and sweet-salty peanut butter. They look bakery-special but are easy to make in one pan—perfect for parties, bake sales, holidays, or just a cozy weekend treat.
Why You’ll Love These Peanut Butter Marshmallow Brownies
- Ultra fudgy texture – Dense, chocolatey brownies with a shiny top.
- Gooey marshmallow pockets – Toasted on top, soft and stretchy inside.
- Peanut butter swirls – Creamy, nutty ribbons that balance the sweetness.
- Crowd-pleasing – Kids and adults both go for seconds.
- Pan-friendly dessert – Bakes in one pan and slices into easy-to-serve bars.
Ingredients
Brownie Base
- 170 g (3/4 cup) unsalted butter, melted and slightly cooled
- 1 1/2 cups granulated sugar
- 2 large eggs + 1 egg yolk, room temperature
- 2 tsp vanilla extract
- 3/4 cup unsweetened cocoa powder
- 3/4 cup all-purpose flour
- 1/2 tsp fine salt
- 1/2 tsp instant espresso powder (optional, for deeper chocolate flavor)
- 1/2 cup semi-sweet chocolate chips or chunks (optional, for extra fudginess)
Peanut Butter Swirl
- 1/2 cup creamy peanut butter (not natural/runny if possible)
- 3 tbsp powdered sugar
- 2–3 tbsp milk or heavy cream (to loosen to swirlable consistency)
Marshmallow Layer
- 2 cups mini marshmallows
or - 1 1/2 cups mini marshmallows + 1/2 cup marshmallow fluff/cream (for extra gooeyness)
Optional Garnish
- Extra chocolate chips or chopped chocolate
- A light sprinkle of flaky sea salt
How to Make Peanut Butter Marshmallow Brownies
1) Prep pan & oven
Preheat the oven to 175°C (350°F).
Line an 8-inch (20 cm) square baking pan with parchment paper, leaving some overhang on the sides so you can lift the brownies out easily after baking.
Tip: Lightly grease the parchment so sticky marshmallow doesn’t cling too much.
2) Make the brownie batter
In a medium bowl, whisk together the melted butter and sugar until glossy and slightly thickened (about 1–2 minutes).
Add the eggs, egg yolk, and vanilla, whisking until the mixture looks thick and well combined.
Sift or whisk together the cocoa powder, flour, salt, and espresso powder (if using) in a separate bowl.
Add the dry ingredients to the wet mixture and fold gently with a spatula just until no dry streaks remain. The batter will be thick.
Fold in chocolate chips or chunks, if using.
Tip: Don’t overmix once the flour is in; this keeps the brownies fudgy, not cakey.
3) Spread and par-bake
Spread the brownie batter evenly into the prepared pan, smoothing the top with an offset spatula or the back of a spoon.
Bake for 15–18 minutes, just until the edges are starting to set but the center is still slightly soft and underbaked.
While the brownies are in the oven, prepare the peanut butter swirl.
4) Make the peanut butter swirl
In a small bowl, stir together peanut butter and powdered sugar.
Slowly add milk or cream, 1 tablespoon at a time, until the mixture is smooth, shiny, and thick but pourable/spoonable (like a thick sauce).
Tip: If it’s too thick to drizzle, add a splash more milk. If it’s too thin, add a bit more peanut butter.
5) Add marshmallows and swirl
Remove the pan from the oven after the initial bake.
Sprinkle the mini marshmallows evenly over the partially baked brownie layer (and dollop marshmallow fluff on top, if using).
Using a spoon, drizzle the peanut butter mixture in lines or random patches over the marshmallows.
With a knife or skewer, gently swirl the peanut butter through the marshmallow and the top surface of the brownie, creating a marbled effect.
6) Finish baking
Return the pan to the oven and bake for an additional 12–18 minutes, or until:
- The edges are set and pulling slightly from the sides,
- The marshmallows are puffed and lightly golden, and
- The center is just set but still slightly soft (it will firm up as it cools).
If the top is browning too quickly, tent loosely with foil for the last few minutes.
Remove from the oven and place the pan on a wire rack.
7) Cool, slice & serve
Let the brownies cool completely in the pan for the cleanest cuts—this can take about 1–2 hours.
Once cool, use the parchment overhang to lift the slab out onto a cutting board.
Use a sharp knife (lightly greased or warmed under hot water and dried) to cut into squares or rectangles.
Serve as is, or slightly warm with ice cream for an extra-indulgent dessert.
Serving Suggestions
- Serve at room temperature for classic chewy-fudgy texture.
- Warm individual squares for a few seconds in the microwave to re-soften the marshmallow.
- Top with a scoop of vanilla, peanut butter, or chocolate ice cream.
- Drizzle with extra melted chocolate or warm peanut butter right before serving.
Cook’s Tips
- Don’t overbake: Slightly underbaked brownies will set as they cool and stay fudgy.
- Pan size matters: An 8-inch pan gives thicker brownies; a 9-inch pan will produce slightly thinner bars and may bake faster.
- Neat slices: Chill the brownies briefly in the fridge before cutting if you want super-clean cuts (especially for photos or gifting).
- Peanut butter type: Use a standard creamy peanut butter; natural, oily peanut butter can separate and won’t swirl as nicely.
- Sticky knife fix: Wipe the knife between cuts and lightly oil it to avoid sticking to marshmallow.
Variations & Add-Ins
- Extra chocolate: Stir in extra chocolate chips or chunks into the batter and sprinkle some on top.
- Crunch factor: Add chopped peanuts, pretzels, or chocolate-covered peanuts for texture.
- Salted PB brownies: Finish with flaky sea salt when the brownies come out of the oven.
- Nut-free option: Swap peanut butter for a seed butter (like sunflower seed butter), keeping in mind the flavor will change.
- S’mores twist: Add a layer of crushed graham crackers on the bottom or sprinkle some on top before baking.
Storage & FAQ
- Storage: Store brownies in an airtight container at room temperature for 2–3 days, or in the fridge for up to 5 days.
- Reheating: Warm briefly in the microwave (5–10 seconds) to re-soften marshmallow and peanut butter.
- Freezing: Freeze individually wrapped squares for up to 2 months. Thaw at room temperature or gently warm before serving.
- Gooey top? That’s normal with marshmallows. Let them cool completely if you want a more set top.
- Can I double the recipe? Yes—double everything and bake in a 9×13-inch pan. Add a few extra minutes to the bake time, watching carefully.
Peanut Butter Marshmallow Brownies give you everything in one bite: fudgy chocolate, gooey marshmallow, and rich peanut butter swirls. They slice beautifully, pack well, and disappear fast—perfect for when you want a dessert that looks impressive but is simple to make.
Peanut Butter Marshmallow Brownies – Fudgy, Gooey & Irresistible
Super fudgy brownies topped with gooey mini marshmallows and creamy peanut butter swirls. These Peanut Butter Marshmallow Brownies are rich, sweet, and slightly salty, making them an irresistible dessert bar for parties, holidays, or any chocolate craving.
Ingredients
- Brownie Base:
- 170 g (3/4 cup) unsalted butter, melted and slightly cooled
- 1 1/2 cups granulated sugar
- 2 large eggs + 1 egg yolk, room temperature
- 2 tsp vanilla extract
- 3/4 cup unsweetened cocoa powder
- 3/4 cup all-purpose flour
- 1/2 tsp fine salt
- 1/2 tsp instant espresso powder (optional)
- 1/2 cup semi-sweet chocolate chips or chunks (optional)
- Peanut Butter Swirl:
- 1/2 cup creamy peanut butter
- 3 tbsp powdered sugar
- 2–3 tbsp milk or heavy cream
- Marshmallow Layer:
- 2 cups mini marshmallows
- or
- 1 1/2 cups mini marshmallows + 1/2 cup marshmallow fluff
Instructions
- 1. Prep pan and oven
- 2. Preheat oven to 175°C (350°F).
- 3. Line an 8-inch (20 cm) square baking pan with parchment, leaving an overhang on two sides. Lightly grease.
- 4. Make the brownie batter
- 5. In a medium bowl, whisk melted butter and sugar until glossy.
- 6. Add eggs, egg yolk, and vanilla; whisk until well combined.
- 7. In another bowl, whisk cocoa powder, flour, salt, and espresso powder (if using).
- 8. Add dry ingredients to wet and fold gently until just combined.
- 9. Fold in chocolate chips if using.
- 10. Par-bake the brownies
- 11. Spread the batter evenly in the prepared pan.
- 12. Bake for 15–18 minutes, until the edges are starting to set but the center is still slightly soft.
- 13. Make the peanut butter swirl
- 14. While brownies bake, stir peanut butter and powdered sugar together in a small bowl.
- 15. Add milk or cream, 1 tablespoon at a time, until smooth and thick but drizzleable.
- 16. Add marshmallows and swirl
- 17. Remove pan from the oven.
- 18. Sprinkle mini marshmallows evenly over the partially baked brownies (add dollops of marshmallow fluff if using).
- 19. Drizzle peanut butter mixture over the top.
- 20. Use a knife or skewer to gently swirl peanut butter through the marshmallow and surface of the brownies.
- 21. Finish baking
- 22. Return pan to the oven and bake another 12–18 minutes, until edges are set, marshmallows are puffed and lightly golden, and the center is just set.
- 23. If browning too quickly, tent loosely with foil.
- 24. Cool and slice
- 25. Cool completely in the pan on a wire rack (for neat slices).
- 26. Lift brownies out using parchment overhang and cut into squares with a sharp, lightly oiled knife.
Notes
For super-clean slices, chill brownies for 30–60 minutes before cutting, then let sit a few minutes at room temperature before serving.
Standard creamy peanut butter (not very oily/natural) gives the best swirl and texture.
If using a 9×9 or 9×13 pan, adjust baking time and expect thinner brownies.
A sprinkle of flaky sea salt on top balances the sweetness beautifully.
Nutrition
Calories: ~320–360
Total Fat: ~18–20 g
Saturated Fat: ~9–10 g
Carbohydrates: ~38–42 g
Sugar: ~30–34 g
Protein: ~5–6 g