Rich, gooey, and irresistible, these Fluffernutter Brownies take everything you love about fudgy brownies and top it with a gooey swirl of peanut butter and marshmallow fluff. The result? An indulgent treat that’s nostalgic and crave-worthy.

I’ve made a lot of brownies over the years. Fudgy, cakey, swirled, topped, stuffed—you name it. But these Fluffernutter Brownies are in a category of their own. I’m not going to lie… I made these brownies three times in one week (in the name of research, of course!) and we were not sad at all about having three batches of fluffernutter brownies to eat and share with friends.

If you’re not familiar with fluffernutter, let me introduce you: a fluffernutter is a sandwich made with peanut butter and marshmallow fluff. I’m not entirely sure I’ve ever had a fluffernutter sandwich, but I love the peanut butter + marshmallow combination. And adding chocolate? Even better!

These peanut butter marshmallow brownies are sweet, salty, creamy, and chewy, all in one bite. The marshmallow fluff caramelizes in the oven and puffs into golden peaks, while the peanut butter melts just enough to swirl beautifully without disappearing into the brownie layer. Every bite hits a different texture: dense, gooey brownie base, stretchy marshmallow, and pockets of rich peanut butter.

These brownies are gooey and sticky and absolutely delicious. My only advice? Make a double batch, because they’ll go fast. If you’re the kind of person who always wanted more filling in your fluffernutter sandwich, you’re going to love this brownie recipe.

Ingredients and Substituions

• Sugar
• Butter: Use unsalted butter for this recipe. To keep the brownies dairy-free, use a vegan butter.
• Cocoa Powder: This recipe is written for Dutch-processed cocoa powder.
• Eggs: For an egg-free version, use flax eggs, but the texture will be a little less rich. (And use an egg-free marshmallow fluff!)
• Vanilla Extract
• All-Purpose Flour: For gluten-free brownies, use a 1:1 gluten-free baking mix with xanthan gum.
• Salt
• Chocolate Chips
• Peanut Butter Chips
• Peanut Butter: Use creamy peanut butter (not natural) for the best swirl and texture.
• Marshmallow Fluff: Use either marshmallow fluff or marshmallow creme, but don’t try to substitute with marshmallows since they won’t spread or puff the same way.

How to Make Fluffernutter Brownies

1. Combine Butter and Cocoa Powder: Melt the butter, then whisk in the cocoa powder and sugar. Add the eggs and vanilla extract.

2. Add the Flour: Stir in the flour, followed by the chocolate chips and peanut butter chips.

3. Spread into Pan: Spread the batter in a parchment-lined baking pan and smooth into an even layer. Dollop spoonfuls of peanut butter and marshmallow fluff over the top, then gently swirl with a knife.

4. Bake the Brownies: Bake until the edges are set and the marshmallow is puffed and gooey. Cool completely before slicing.

Toasted Marshmallow Fluff

When you bake marshmallow fluff on top of brownies, something magical happens: it puffs, it browns, and it transforms into a sticky, gooey topping with golden edges and chewy centers. It’s part marshmallow, part meringue, and totally irresistible. If you’ve ever wondered what causes marshmallow fluff to rise and brown in the oven, we can answer that with my favorite subject… kitchen chemistry!

Kitchen Chemistry

Marshmallow fluff is a whipped mixture of sugar, water, and egg whites. The egg whites stabilize tiny air bubbles during mixing, just like in a meringue. When the fluff is baked, heat causes the water inside to evaporate and the trapped air to expand, making the fluff puff up. As the water continues to evaporate, the structure dries out just enough to hold its shape—light, airy, and full of volume.

Because marshmallow fluff is already whipped and aerated, it expands quickly when heated, puffing up into soft peaks and chewy edges. The result is a gooey, caramelized topping that adds both texture and flavor contrast to the dense, fudgy brownies underneath. Paired with pockets of melted peanut butter that soften and swirl into the fluff, the topping turns into a sticky-sweet, salty-creamy crown for every bite.

Tips and Tricks for the Best Fluffernutter Brownies

1. Room Temperature Eggs: Let your eggs sit out for 20-30 minutes before baking so they mix more smoothly into the batter.
2. Warm Peanut Butter: Warm the peanut butter in the microwave for 10 seconds to help it spread more easily and swirl into the marshmallow fluff.
3. Swirl Gently: Use a butter knife or skewer to lightly swirl the toppings without fully blending them into the brownie batter.
4. Cool Completely: Let the brownies cool fully to allow the topping to set and prevent a gooey mess while cutting.
5. Clean Slices: For the cleanest presentation, refrigerate the brownies before cutting and use a sharp knife wiped clean between each cut.
6. Double the Recipe: These brownies are so good, you should probably just go ahead and make a 9×13-inch pan! To fill the pan, multiply all the ingredients by 1.5 and add an extra 3-5 minutes to the baking time.
7. Storage: Store the brownies at room temperature for 3-4 days. Refrigerate if you prefer a firmer topping. The brownies can be frozen for up to 3 months.
8. Recommended Tools: 9×9-inch Metal Pan | Parchment Paper | Mixing Bowls | High-Quality Dutch Processed Cocoa Powder | Marshmallow Fluff

More Brownie Recipes:

• Peanut Butter Oreo Brownies
• Caramel Pecan Turtle Brownies
• Cookie Dough Brownies
• Peanut Butter Stuffed Brownies
• Ultimate Nutella Brownies
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