Ultimate Marshmallow Peanut Butter Brownies (Chewy, Gooey Dessert That Steals the Show)

This Marshmallow Peanut Butter Brownies recipe is decadent, chewy, and ridiculously easy. It takes about 1 hour total and serves 9–12.

Okay, picture this: warm brownies with a fudgy peanut butter core and a pillowy marshmallow swirl that oozes when you cut into it. Tempting, right? I first made these on a rainy Saturday when I needed something to cheer me up, and they absolutely delivered—my neighbors showed up unannounced, and I didn’t even pretend surprise. Spoiler: they disappeared within an hour. In this post, I’ll walk you through every step, share my pro tips, and give fun topping ideas so you can impress without sweating it.

Why You’ll Love This Recipe

• Layers of texture: fudgy brownies, creamy peanut butter filling, and fluffy marshmallow swirl.
• Fast and forgiving: the recipe tolerates small mistakes—thankfully.
• Great for sharing: serve at parties, potlucks, or when you want to bribe someone.
• Flexible: swap chocolate types or add nuts without breaking the magic.
• Makes a statement: people always ask for the recipe. Seriously.

Ingredients You’ll Need

• 1/2 cup Creamy Peanut Butter
• 1/4 cup Powdered Sugar
• 2 tbsp Unsalted Butter (room temperature)
• Pinch of Salt
• 1 cup + 2 tbsp All-Purpose Flour
• 3/4 tsp Salt
• 1/2 tsp Baking Powder
• 4 Large Eggs (room temperature)
• 1 1/2 cups Granulated Sugar
• 1/2 cup Brown Sugar (packed)
• 1/2 cup Canola Oil
• 2 tsp Pure Vanilla Extract
• 8 tbsp Unsalted Butter
• 8 oz Bittersweet Chocolate (chopped)
• 1/4 cup Dutch Process Cocoa Powder
• 1/2 cup Store-Bought Marshmallow Fluff

Ingredient and Method (Didactic)

• Ingredient: Use the list above. I recommend fresh eggs and good bittersweet chocolate for the best flavor.
• Method: You’ll make a simple peanut butter filling, pour the brownie batter, then swirl marshmallow fluff on top before baking. Keep everything organized and you’ll finish faster than you think.

How to Make (Step-by-Step)

STEP 1 — Peanut Butter Filling

1. Combine 1/2 cup creamy peanut butter, 1/4 cup powdered sugar, 2 tbsp room-temperature unsalted butter, and a pinch of salt in a bowl.
2. Beat until smooth and spreadable. I use a small spatula and taste-test (don’t judge).
3. Chill the filling briefly if it feels too soft—this helps it hold shape when you add it to the batter.

STEP 2 — Brownies

1. Preheat oven to 350°F (175°C) and line an 8×8-inch pan with parchment. I always grease the pan lightly so the parchment stays put.
2. Melt 8 tbsp unsalted butter with 8 oz bittersweet chocolate over a double boiler or in short microwave bursts. Stir until glossy and cool slightly.
3. Whisk 4 large room-temp eggs, 1 1/2 cups granulated sugar, and 1/2 cup packed brown sugar until combined and slightly aerated.
4. Stir in 1/2 cup canola oil and 2 tsp vanilla extract. Pour in the chocolate mixture and whisk until uniform.
5. Sift in 1 cup + 2 tbsp all-purpose flour, 3/4 tsp salt, 1/2 tsp baking powder, and 1/4 cup Dutch-process cocoa powder. Fold gently until you see no dry streaks. Don’t overmix—gluten wants to ruin chewy brownies.

STEP 3 — Assembling the Marshmallow Peanut Butter Brownies

1. Pour half the brownie batter into the prepared pan and smooth it out.
2. Drop dollops of the peanut butter filling across the batter, spacing them evenly.
3. Spoon the remaining brownie batter over the peanut butter—don’t worry about perfect coverage.
4. Warm 1/2 cup marshmallow fluff for 10–15 seconds in the microwave so it becomes pourable. Dollop the fluff on top and use a butter knife to swirl gently into the batter—do not stir.
5. Bake for 30–35 minutes, or until a toothpick in the brownie part (not the marshmallow or peanut butter) comes out with a few moist crumbs. Cool before slicing or else the layers will squish everywhere—tempting, but messy.

Pro Tips for the Best Results

• Use room-temperature eggs to help the batter emulsify properly.
• Don’t overbake; remove the brownies when a toothpick still shows moist crumbs. They firm up as they cool.
• Warm the marshmallow fluff so it swirls smoothly—cold fluff clumps and refuses to play nice.
• Chill the peanut butter filling if it gets too soft; it holds shape better.
• Cut with a hot knife (run under hot water and wipe dry) for clean slices. Trust me, aesthetics matter.
• FYI: You can swap canola oil for melted coconut oil if you want a hint of tropical flair.

Fun Variations & Topping Ideas

Variations:

• Nutty Twist: Fold chopped roasted peanuts into the peanut butter filling for crunch.
• Double Chocolate: Use milk chocolate instead of bittersweet for a sweeter, softer edge.
• Salted Caramel: Add a thin layer of caramel under the marshmallow swirl for grown-up decadence.

Toppings:

• Sea salt flakes to contrast the sweet with a savory pop.
• Mini chocolate chips for extra melty pockets.
• Crushed pretzels for a salty, crunchy finish.
• Drizzle of melted peanut butter or chocolate to make it look like you tried very hard (even if you didn’t).

Storing and Reheating

Storing:

• Store leftover brownies in an airtight container at room temperature for up to 3 days.
• Refrigerate for up to 5 days, but bring to room temp before serving so the marshmallow softens.

Reheating:

• Warm a single slice in the microwave for 10–15 seconds to revive gooeyness.
• Use a low oven (300°F / 150°C) for 5–8 minutes if you want a larger batch warmed evenly.

Leftover ideas

• Brownie ice cream sandwiches: Slice thin and press ice cream between two squares.
• Brownie trifle: Layer chunks with whipped cream and berries for an over-the-top dessert.
• Milkshake booster: Blend a brownie square into your chocolate milkshake for instant happiness.
• Crumble topping: Crumble and sprinkle over vanilla pudding or yogurt.

Frequently Asked Questions (FAQ)

Can I use natural peanut butter?

Yes, but natural peanut butter contains oil that separates. I recommend stirring it well and chilling the filling briefly so it firms up. IMO, creamy commercial peanut butter gives a more reliable result.

Can I make this gluten-free?

You can swap a 1:1 gluten-free flour blend for the all-purpose flour. Expect slightly different texture—still delicious, but a touch crumbly.

Can I freeze these brownies?

Absolutely. Wrap cooled squares tightly and freeze for up to 2 months. Thaw in the fridge overnight or at room temp for a couple hours.

What if my marshmallow fluff melts too much and sinks?

That happens when the oven runs hot. Try swirling the fluff lightly and bake at 350°F. If you consistently have sinking, reduce oven temp by 10–15°F and bake a little longer.

Conclusion

If you crave jaw-dropping fudge with a creamy peanut butter heart and a cloud of marshmallow on top, these Marshmallow Peanut Butter Brownies deliver on every level. I promise they impress guests, save bad days, and pair nicely with cold milk or stubbornly strong coffee. Ready to make them? Try the recipe once and you’ll find reasons to make it again—trust me, you will.

For a similar take and extra inspiration, check out Peanut Butter Marshmallow Swirl Brownies – The Vanilla Bean Blog for more photos and variations. I’d love to hear how your batch turned out—leave a comment and rate the recipe if you try it!