Fudgy Brownies with Marshmallow Fluff Swirl

These extra-fudgy marshmallow-fluff brownies are studded with chocolate chips and chopped pecans. Rich and indulgent, these rocky-road-style brownies take about 20 minutes to prepare and bake to a glossy, crackly top with a tender, molten interior.

Note: This recipe was originally published in February 2021 and has been updated with refined measurements and new photos.

If you love ultra-fudgy brownies, these marshmallow-swirl brownies combine everything great about a dense chocolate base with sweet marshmallow ribbons and the crunch of pecans. The marshmallow fluff adds a pillowy, slightly chewy contrast to the deep chocolate, while chopped pecans and mini chocolate chips give texture and more chocolate flavor. They’re a fantastic treat for brownie fans and anyone who loves rocky road-style desserts.

Ingredient Notes

Cocoa powder: Dutch-processed cocoa is used here for a smoother, less acidic chocolate flavor. If your cocoa lists “alkali” or “processed with alkali” it is Dutch-processed; otherwise it’s likely natural cocoa.

Marshmallow fluff: Marshmallow cream, marshmallow creme or marshmallow fluff all work interchangeably for the swirl.

Oil: Use a neutral-tasting oil such as vegetable or canola oil. Avoid using flavored oils that could compete with the chocolate.

Butter: Unsalted butter is recommended so you can control the salt level. European-style butter with higher butterfat yields a richer texture if available.

Chocolate: Choose a good-quality dark chocolate to balance the sweetness of the marshmallow.

Step by Step Instructions

Step 1: Preheat the oven to 350°F (175°C). Line an 8×8-inch square baking pan with aluminum foil, leaving an overhang to lift the brownies out after cooling.

Step 2: In a small bowl, whisk together the all-purpose flour and kosher salt. Set aside.

Step 3: Melt the butter in a microwave-safe bowl in short increments or melt over a double boiler. Add the chopped dark chocolate to the hot butter and let it sit for a minute, then stir until smooth. If needed, warm briefly again in the microwave in 15–20 second bursts. Allow the chocolate-butter mixture to cool slightly while you prepare the sugar and eggs.

Step 4: In a stand mixer fitted with the whisk attachment, or with a hand mixer, whisk the eggs, extra egg yolk, granulated sugar, light brown sugar, neutral oil and vanilla extract on medium-high speed for about 6–8 minutes. Whisking until small bubbles form on the surface helps create a thin, shiny crust on top of the brownies.

Step 5: Stir the cocoa powder into the melted chocolate until smooth. Pour the egg-and-sugar mixture into the chocolate and fold together until combined. Fold in the flour and salt until no streaks remain, then fold in most of the chopped pecans and chocolate chips, reserving a small handful of each for the top.

Step 6: Transfer the batter to the prepared pan and smooth the top. Drop spoonfuls of marshmallow fluff over the batter, then swirl gently with a toothpick or the tip of a knife to create ribbons of marshmallow through the brownies. Sprinkle the reserved chopped pecans and chocolate chips over the surface.

Step 7: Bake at 350°F (175°C) for 25–30 minutes. A toothpick inserted should come out with a few moist crumbs but not wet batter. Allow the brownies to cool completely in the pan before lifting out with the foil overhang and cutting into 9 or 12 squares.

Recipe Tips & Tricks

• Use a kitchen scale: Weighing ingredients produces the most consistent results. Baking by weight is more accurate than cup measures.
• Flour measuring: If you must use cups, use the “fluff and sweep” method—fluff the flour in its container, spoon into your cup lightly, and level—so you don’t pack too much flour into the measuring cup.
• Substitutions: Swap pecans for walnuts or another favorite nut, or omit nuts entirely. If you prefer mini marshmallows to marshmallow fluff, add them during the final 5 minutes of baking so they melt and toast slightly. Chocolate chips can be substituted with peanut butter or butterscotch chips. For a s’mores variation, replace pecans with crushed graham crackers.

Recipe