Some desserts make an entrance, and these fudgy marshmallow mud brownies are one of those trays that never make it to the table intact. I first baked them for a backyard movie night when I wanted something seriously chocolatey but playful enough to delight the kids. The shiny, crackly brownie top gives way to a soft middle, then a pillowy marshmallow layer, all sealed with a pour-over chocolate icing that sets into a glossy shell. Every square feels like a little celebration.

What makes them special to me is the texture journey. You get dense, fudgy brownie punctuated by little pockets of melted chocolate, a cloudlike marshmallow cap, and a silky, just-set icing that snaps ever so slightly when you cut it. I learned a few tricks along the way: gently emulsifying butter and sugar for a shiny top, baking in a metal pan for even heat, and finishing the whole thing with a quick cocoa icing while the marshmallows are still warm. When I carried the first batch outside, I watched friends circle the pan, forks at the ready, as if we were cutting a celebratory cake. It has been our go-to party sweet ever since.

Ingredients

• Unsalted butter: Use a quality high-fat butter like Kerrygold for rich flavor and a glossy brownie top. Cut into pieces so it melts evenly without scorching.
• Granulated sugar: Domino works beautifully; the fine crystals help the butter-sugar emulsion and contribute to that crackly crust on top.
• Canola oil: Just a touch keeps the brownies plush without making them cakey, adding moisture that stays even after cooling.
• Vanilla extract: A full tablespoon rounds out the cocoa and dark chocolate notes and adds warmth to the marshmallow layer.
• Large eggs: Room temperature eggs incorporate more easily, building structure while keeping the crumb fudgy.
• All-purpose flour: King Arthur’s consistent protein level ensures structure without tipping into cakey territory; do not overmix.
• Dutch-process cocoa powder: Ghirardelli Dutch-process offers smooth, deep chocolate flavor and a beautiful dark color.
• Salt: A small amount sharpens chocolate notes and balances the sweetness of marshmallows and icing.
• Dark or milk chocolate: Chopped bar chocolate (Trader Joe’s Pound Plus is perfect) melts into pockets and adds lush texture.
• Mini marshmallows: They melt into a soft, stretchy layer that holds the icing and gives classic mud brownie flair.
• Powdered sugar and cocoa: Whisked into warm butter for a pourable icing that sets smooth and shiny.
• Whole milk and vanilla: Thins the icing to the perfect texture and infuses gentle sweetness.

Instructions

Prepare the pan: Heat oven to 350°F. Line a metal 9x13-inch pan with two sheets of parchment, one lengthwise and one crosswise, leaving overhang for easy lifting. Lightly coat the parchment with cooking spray to prevent sticking at the corners. Emulsify butter and sugar: Melt 1 cup unsalted butter in a heavy-bottomed saucepan over low heat. Stir in 2 1/2 cups granulated sugar until the mixture looks glossy and no butter pools separately. Remove from heat and stir for 3 to 5 minutes to release heat and start dissolving sugar crystals. Add oil and vanilla: Stir in 2 tablespoons canola oil and 1 tablespoon vanilla until fully combined. The mixture should look cohesive with no oil floating on top. Proper emulsification helps create a shiny, crackly top. Incorporate eggs: Beat in 5 large eggs one at a time with a spatula or fork, mixing until each egg disappears before adding the next. Avoid whipping in excessive air; you are aiming for smooth and glossy, not airy. Sift in dry ingredients: Sift 1 cup all-purpose flour, 3/4 cup plus 1 tablespoon Dutch-process cocoa, and 3/4 teaspoon salt over the wet mixture. Fold gently just until no dry streaks remain. Overmixing toughens brownies. Fold in chocolate: Fold most of the 8 ounces chopped chocolate into the batter, reserving a small handful for the top. Distribute evenly so each slice gets melty pockets. Bake the brownies: Spread batter into the prepared pan and sprinkle on remaining chocolate. Bake for 25 minutes. The center should look just set at the edges with a slight jiggle in the very middle. Add marshmallows: Remove the pan and immediately scatter 6 cups mini marshmallows evenly over the top. Return to the oven for 3 minutes to soften and fuse the marshmallows into a uniform layer. Make the icing: In a saucepan over medium heat, melt 6 tablespoons salted butter. Whisk in 2 1/2 cups powdered sugar and 2 tablespoons unsweetened cocoa. Gradually whisk in 1/4 cup whole milk and 2 teaspoons vanilla until smooth and pourable. Glaze and set: Remove icing from heat and immediately pour over the warm marshmallows, spreading gently with a spatula to cover. The icing will begin to set within minutes. Let cool until fully set. Slice and serve: Lift from the pan using the parchment. For clean cuts, use a plastic knife or a sprayed and wiped metal knife. Cut into 20 to 24 squares and enjoy.

Storage Tips

Let the brownies cool until the icing is completely set and the marshmallow layer no longer feels tacky, then transfer the slab to a cutting board and portion as desired. Store squares in a single layer in an airtight container at room temperature for up to 2 days, or refrigerate for 4 to 5 days with parchment between layers. For longer storage, freeze in a single layer on a sheet pan until firm, then pack into freezer-safe containers for up to 2 months. Thaw overnight in the refrigerator or for about 30 minutes at room temperature. To revive the fudginess, rest at room temperature 10 to 15 minutes before serving.

Ingredient Substitutions

If you only have natural cocoa powder, use the same amount but expect a slightly lighter color and a touch more bitterness; add 1 extra teaspoon vanilla to round it out. For gluten-free, swap in a cup-for-cup gluten-free baking blend with xanthan gum. No canola oil? Use neutral vegetable oil at a 1:1 ratio. You can choose all dark or all milk chocolate, or a mix. If you are out of mini marshmallows, cut large marshmallows into quarters and use the same volume. For a less sweet topping, reduce powdered sugar by 1/4 cup and increase cocoa by 1 teaspoon to taste.

Serving Suggestions

These brownies shine on a dessert board with fresh strawberries, raspberries, and salted nuts for contrast. For parties, sprinkle the icing with a whisper of flaky salt or rainbow sprinkles before it sets. In cooler months, serve warm squares with a scoop of vanilla or coffee ice cream. For summer picnics, cut them smaller into bite-size squares for easy finger food. If you are going festive, add crushed peppermint on top in December or toasted chopped pecans for a Southern twist.

Cultural Background

Brownies are a classic American invention, loved for their dense texture and rich chocolate hit. The marshmallow-and-icing-topped version nods to the famed Mississippi mud desserts, where layers of chocolate, marshmallow, and fudge-like toppings mimic the indulgent mud pies of Southern lore. Dutch-process cocoa, while European in origin, became a pantry staple in the States, creating that smooth, deep chocolate flavor many of us crave. This pan captures that cross-current of American nostalgia and European cocoa craftsmanship.

Seasonal Adaptations

In spring, fold in 1/2 cup chopped toasted almonds or pecans with the chocolate for crunch. Summer calls for a peanut butter swirl: dollop 1/3 cup warmed peanut butter over the brownie batter, swirl lightly, then bake and finish as directed. In fall, stir 1 teaspoon espresso powder into the batter to deepen chocolate notes and top the icing with a pinch of cinnamon. During the holidays, sprinkle crushed peppermint or candied pecans over the icing before it sets for a festive finish.

Meal Prep Tips

For events, bake the brownies the day before and let the icing set completely. Slice with a plastic knife, then store in a single layer in a lidded container. Transport directly in the pan if you need extra stability. If making ahead for lunch boxes, wrap individual squares in parchment for grab-and-go portions. To refresh, let refrigerated brownies sit at room temperature 15 minutes so the fudgy texture softens. For a warm treat, microwave one square for 10 to 12 seconds to lightly loosen the marshmallow layer.

From quiet weeknights to big celebrations, this pan never fails to bring a little wonder to the table. I hope it becomes your family’s new chocolate tradition, one glossy square at a time.