There are desserts that take you straight back to warm kitchens and busy family gatherings, and these fudgy Mississippi Mud Brownies do exactly that for me. I first made them for a summer potluck when I needed something indulgent, sturdy enough to travel, and guaranteed to delight both kids and adults. That marshmallow layer seals the deal: it melts into a pillowy blanket over the brownies, then gets cloaked in a quick, satiny cocoa icing that sets into a perfect sliceable top. The contrast of textures is irresistible, from the chewy edges to the gooey center and soft marshmallow bite.

I have a soft spot for this version because it leans unapologetically fudgy. Kerrygold unsalted butter brings rich flavor, while Domino sugar dissolves into the butter for that classic shiny top. Dutch-process cocoa (I love Ghirardelli) deepens the chocolate without bitterness, and a handful of chopped chocolate from a Trader Joe’s Pound Plus bar creates pockets of molten goodness. Over the years, these brownies have earned a regular spot in my rotation for birthdays, bake sales, and casual Friday nights. The first slice always goes to the impatient person hovering by the counter—usually me.

Ingredients

• Unsalted butter: Choose a high-fat butter like Kerrygold for deep dairy flavor and a tender crumb. Melt gently to keep the emulsion smooth and help the sugar dissolve for a glossy top.
• Granulated sugar: Domino’s fine crystals dissolve well in warm butter. Proper emulsification ensures a crackly surface and dense, fudgy interior without graininess.
• Canola oil: A touch of neutral oil enhances moisture and fudginess. It remains soft at room temperature, preventing the brownies from drying out.
• Vanilla extract: Real vanilla rounds out the chocolate and adds warmth. Look for pure extract; the aroma lifts both the brownie base and the icing.
• Large eggs: Vital Farms eggs whisk in one at a time for structure and sheen. Proper mixing creates that signature shiny crust.
• All-purpose flour: King Arthur’s consistent protein level keeps the brownies sturdy but tender. Measure lightly and avoid overmixing for dense, fudgy results.
• Dutch-process cocoa powder: Ghirardelli Dutch-process brings smooth, dark chocolate flavor and deep color without harsh bitterness.
• Salt: A little fine salt sharpens the chocolate notes and balances the sweetness throughout the layers.
• Chocolate bar or chips: Chopped pieces from a Trader Joe’s Pound Plus bar melt into puddles and create luscious pockets in every bite.
• Mini marshmallows: The classic Mississippi mud layer. They soften and meld into the brownie surface in just a few minutes.
• Powdered sugar: Whisks into a silky icing. Sifting prevents lumps and keeps the pour smooth.
• Unsweetened cocoa powder: Reinforces the chocolate flavor in the icing for a balanced, not-too-sweet finish.
• Whole milk: Just enough to loosen the icing to a pourable consistency while staying glossy.
• Salted butter (for icing): Adds a welcome hint of salt to offset the marshmallow sweetness and enrich the icing texture.

Instructions

Prepare the pan and preheat: Heat the oven to 350°F. Line a metal 9 by 13 inch pan with parchment, leaving overhang on two sides for easy lifting. Lightly spray with cooking spray. Layer the parchment so the shorter sheet sits under the longer, ensuring clean corners and simple removal. Emulsify butter and sugar: Melt the unsalted butter over low heat in a heavy saucepan. Stir in granulated sugar until the mixture looks glossy and unified with no separated butter. Remove from heat and stir for about 5 minutes to cool slightly while keeping the emulsion stable and smooth. Add oil, vanilla, and eggs: Stir in canola oil and vanilla until there’s no visible separation. Add eggs one at a time, mixing thoroughly after each. You’re building a thick, shiny batter that traps air just enough for a crackly top without sacrificing fudginess. Combine dry ingredients: Sift flour, Dutch-process cocoa, and salt directly into the pot. Gently fold with a spatula just until no dry streaks remain. Avoid overmixing, which can create a cakey texture instead of dense, fudgy squares. Add chocolate and bake: Fold most of the chopped chocolate into the batter. Spread into the prepared pan and scatter remaining pieces on top. Bake for 25 minutes; the edges will look set, and the center should be soft but not liquid. Marshmallow layer: Remove the pan and scatter mini marshmallows evenly over the surface. Return to the oven for 3 minutes, just until the tops look slightly puffed and glossy. Do not toast deeply; they should be soft and melty. Make icing and finish: Melt salted butter over medium heat. Whisk in sifted powdered sugar and cocoa, then whisk in whole milk and vanilla until smooth and pourable. Immediately pour over marshmallows, nudging gently with a spatula to cover. Let set completely before lifting and slicing.

Storage Tips

Cool the slab completely before lifting from the pan and slicing. Store squares in a single layer or with parchment between layers in an airtight container at room temperature for 3 to 4 days. For longer storage, freeze on a sheet tray until firm, then transfer to freezer bags with the air pressed out; they keep up to 3 months. To serve, thaw at room temperature 1 to 2 hours. Avoid refrigeration, which can dry the crumb and harden the icing. If you like a slightly warm bite, microwave an individual square for 8 to 10 seconds—just enough to soften the marshmallow again.

Ingredient Substitutions

If you only have natural cocoa, use the same amount; expect a slightly lighter color and a touch more bitterness. Semi-sweet chips can stand in for chopped chocolate, though chopped bars melt into softer puddles. No canola oil? Use vegetable or light olive oil. Salted butter in the batter is fine—simply reduce added salt to a scant 1/2 teaspoon. For the icing, you can swap 2 to 3 tablespoons of the milk with hot coffee to intensify chocolate flavor. If you must use a glass pan, lower the oven temperature to 325°F and extend bake time by 5 to 8 minutes, checking often.

Serving Suggestions

These are sensational on their own, but a small scoop of vanilla or coffee ice cream sets off the fudgy crumb. For a party platter, cut smaller 1 1/2 inch squares and arrange in a tight grid, then dust lightly with cocoa powder for a bakery look. A drizzle of warm caramel is a fun, sticky twist. In summer, serve with fresh strawberries or raspberries; their tartness balances the sweetness. For a birthday dessert board, add bowls of toasted pecans and crushed pretzels so guests can sprinkle a crunchy finish on their slices.

Cultural Background

Mississippi mud sweets trace their roots to Southern kitchens, named for the dense, rippled look that resembles riverbank mud. The classic combination involves a fudgy base, marshmallow blanket, and chocolate icing, though some regions add nuts or swap the brownie for cake. This brownie-forward version leans on the tradition of rich, crowd-pleasing desserts that travel well and slice neatly for gatherings. Over time, the style spread far beyond the South, becoming a potluck staple wherever chocolate lovers congregate. It is a dessert that asks for paper plates, good company, and a second square.

Seasonal Adaptations

In winter, add 1/2 teaspoon peppermint extract to the icing for a hot-cocoa vibe and sprinkle with crushed candy canes. In spring, swirl 1/4 cup raspberry jam onto the brownie batter before baking for tart ribbons. Summer calls for fresh berry sides and smaller squares. For fall, fold in 3/4 cup toasted pecans and a pinch of cinnamon to the batter for warmth. Holiday parties love a drizzle of salted caramel over the set icing, or a scatter of mini chocolate chips while the icing is still soft.

Meal Prep Tips

Bake the brownie base a day ahead, cool, cover, and hold at room temperature. About an hour before serving, rewarm in a 300°F oven for 5 minutes, add marshmallows for 3 minutes, then finish with the icing. To portion for lunchboxes, cut once the icing sets and wrap squares individually in parchment or plastic wrap. For large events, double the recipe and bake in two separate metal pans to ensure even cooking; do not attempt a single thicker pan, which risks underbaking the center.

Success Stories

One of my favorite bake sale memories was watching a hesitant buyer circle the table, choose a square, then come back immediately to purchase three more “just in case.” Another time, I brought a pan to a moving day and it powered an entire crew of friends through the last boxes. These brownies have that rare, reassuring quality: they feel homemade and nostalgic while looking polished and party-ready. Keep this one in your back pocket; it rarely fails to make someone’s day.

If chocolate comfort is what you crave, this pan delivers every time. Bake a batch, share it generously, and enjoy the quiet moment when the glossy icing cracks under your knife and the marshmallow sighs beneath it—that’s the sweet spot.