About this recipe
If there are three things I’ll never turn down, it’s brownies, peanut butter, and marshmallow fluff. Peanut butter and chocolate are already a match made in heaven, and marshmallow has always belonged with chocolate, so this recipe was begging to be created!
These bars start with a layer of rich, fudgy brownies swirled with ribbons of nostalgic marshmallow fluff (which I could happily eat straight from the jar…slightly concerning, but incredibly comforting- IYKYK!). Then they’re topped with generous globs of peanut butter cookie dough that bake right alongside the brownies.
The whole pan is baked low and slow so the brownie batter and cookie dough bake in perfect unison. The result is the fudgiest brownies with tender pockets of peanut butter cookie, gooey swirls of marshmallow, and that perfect sweet-and-salty combination in every bite. If you’re a fluffernutter fan, you have to try these bad boys!
Key Ingredients
Unsalted Butter — Used in both the brownie and peanut butter cookie dough layers, butter adds richness, moisture, and that melt-in-your-mouth texture. It helps create fudgy brownies with a glossy finish and keeps the cookie dough soft and tender once baked together.
Brown & Granulated Sugar — These two sugars work together in both layers to build sweetness, structure, and texture. Brown sugar adds moisture, chewiness, and a subtle caramel depth, while granulated sugar helps create that classic shiny brownie top and balances the softness of the cookie dough.
High-quality cocoa powder & chocolate chips — A rich cocoa powder gives the brownies their deep chocolate base, while chocolate chips melt into pockets of gooey chocolate throughout. Together, they create layered chocolate flavor in every bite that is bold, smooth, and slightly melty in all the right places.
Creamy Peanut Butter — I love using Jif or Skippy here- because they bring nostalgia and familiarity to the cookie dough layer. They deliver that signature sweet-salty flavor that pairs perfectly with chocolate and marshmallow, making the dessert feel like a childhood favorite turned bakery-style treat.
Egg Yolks — Used in both components, egg yolks add richness, tenderness, and a soft, fudgy structure. They enhance the brownie’s dense texture while keeping the cookie dough soft and rich without making it heavy or dry.
Cornstarch — A small but important ingredient in both layers, cornstarch helps refine texture and keep everything soft-baked. In the brownies, it contributes to a slightly fudgier bite, while in the cookie dough it ensures a tender, delicate crumb.I also believe that cornstarch ensures freshness in these brownies long after they have baked.
Baking Soda — Added to the peanut butter cookie dough, baking soda provides light lift and encourages gentle spread. It also enhances browning and balances sweetness, helping the cookie layer taste more rounded and bakery-style.
Marshmallow Fluff & Nutter Butters — The essential toppings for this recipe! They make this dessert extra indulgent and more importantly… so nostalgic! Marshmallow fluff melts into gooey swirls across the top, while Nutter Butters add crunch, extra peanut butter flavor, and a playful, familiar cookie-inspired finish.
FAQ’s
Helpful Tips
- Whisk the eggs and sugar vigorously for brownies: This step helps create that shiny, crinkly top and improves overall texture.
- Don’t overmix after adding flour: Once the dry ingredients are added, fold gently to keep the brownies fudgy instead of cakey.
- Chill the peanut butter dough slightly if it’s too soft: This makes it easier to scoop and layer on top of the brownies.
- Leave some brownie exposed on top: It helps create those gooey “pockets” where marshmallow and cookie dough bake into the surface.
- Use parchment overhang: This makes lifting the brownies out of the pan clean and easy for slicing.
- Cool completely before cutting: This is key for clean slices and the best texture—especially with the marshmallow layer.
More Recipes!
Here are some more recipes you might enjoy!
Toasted Marshmallow Brownie Loaf
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Fluffernutter Brownies
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Equipment
- Hand mixer or stand mixer (with paddle attachment)
Ingredients
Brownies
- 3/4 cup (170 g) unsalted butter, melted
- 3/4 cup + 3 tbsp (188 g) granulated sugar
- 1/3 cup + 1 tbsp (83 g) packed light brown sugar
- 1/2 cup (41 g) cocoa powder
- 2 large eggs + 1 large egg yolk
- 1 tsp (5 g) vanilla extract
- 1/4 tsp (1.5 g) salt
- 3/4 cup (90 g) all-purpose flour, gently spooned & leveled, not packed
- 1 tsp (3 g) cornstarch
- 3/4 cup (128 g) semisweet chocolate chips
- 1/2 tsp (1 g) espresso powder
- 1/2 cup (65 g) marshmallow fluff
Peanut Butter Cookies
- 1/3 cup (85 g) creamy peanut butter, I like to use Jif
- 2 1/2 tbsp (34 g) unsalted butter
- 3 tbsp + 1 tsp (40 g) packed light brown sugar
- 1 tbsp + 1 tsp (15 g) granulated sugar
- 1 large egg yolk
- 1/4 tsp (1 g) vanilla extract
- 1/4 tsp (1 g) baking soda
- 1/4 tsp (1 g) cornstarch
- pinch of fine sea salt
- 1/2 cup + 1 tbsp (65 g) all-purpose flour, gently spooned & leveled, not packed
- Nutter Butter Cookies (for topping after baking)
Instructions
Enable Step-by-Step Mode- Preheat oven to 325°F (163°C). Line a 9×9-inch pan with parchment paper, leaving overhang on two sides for easy removal.
- For the brownie layer, in a medium bowl, whisk together the flour, cocoa powder, cornstarch, espresso powder, and salt. Set aside.
- In a separate large bowl, whisk the melted butter with the granulated sugar and brown sugar until fully combined and glossy.
- Add the eggs, egg yolk, and vanilla extract. Whisk vigorously for 30–60 seconds until the mixture thickens slightly and looks smooth and shiny.
- Gently fold the dry ingredients into the wet mixture using a spatula until just combined. Do not overmix. Fold in the semisweet chocolate chips. Spread the brownie batter evenly into the prepared pan.
- For the pb cookies, in a mixing bowl, use a hand mixer to beat the peanut butter and butter together until smooth and creamy. (about 30 seconds)
- Add the brown sugar, granulated sugar, egg yolk, and vanilla extract. Mix until well combined and fluffy.
- Add the flour, baking soda, cornstarch, and salt. Mix on low or fold gently until a soft dough forms. Do not overmix.
- Drop spoonfuls of the 1/2 cup of marshmallow fluff over the brownie batter. Scoop small chunks of peanut butter cookie dough and scatter them over the top like a cobbler, pressing lightly into the surface- this helps the brownies and cookie dough bake together without separating. ** Leave some brownie visible so it bakes in pockets.
- Bake for 40 – 42 minutes, or until the edges are set and the center is slightly soft but not jiggly. After baking, top with some nutter butter cookies- if desired!
- Allow to cool completely in the pan before lifting out using the parchment overhang and slicing. Enjoy!