Brownie layer
- 1 cup butter
- 2 cups granulated sugar
- 4 large eggs
- 1 teaspoon vanilla extract
- 1/3 cup unsweetened cocoa powder
- 1 1/2 cups all-purpose flour
- 1/4 teaspoon salt
- 1 cup chopped pecans
- 4 cups mini marshmallows
These quantities closely mirror Mississippi mud cake and brownie bases that start with melted or softened butter, cocoa, sugar, eggs, flour, and nuts baked in a shallow pan. Mini marshmallows are added after baking (or near the end) so they melt into a pillowy top layer.
Chocolate frosting
- 1/2 cup butter
- 1/3 cup unsweetened cocoa powder
- 1/3 cup milk
- 1 teaspoon vanilla extract
- 3 1/2 cups powdered sugar
This frosting is similar to the pourable chocolate icing used in many Mississippi mud cake recipes, made by melting butter with cocoa and milk, then whisking in powdered sugar and vanilla until smooth.
Step-by-step instructions
1. Prep the pan and oven
Preheat the oven to 350°F (175°C). Grease a 9×13-inch baking pan (or line with parchment, leaving an overhang for easy removal). Most Mississippi mud cakes and brownies are baked in this size pan to get a relatively thin, rich layer that supports the toppings.
2. Make the brownie batter
In a large mixing bowl, beat or whisk together the 1 cup butter and 2 cups granulated sugar until well combined and smooth. Many recipes use melted butter; if yours is melted and slightly cooled, whisk it directly with the sugar.
Add the 4 eggs, one at a time, beating well after each addition, then mix in 1 teaspoon vanilla extract until the mixture is thick and glossy. This method mirrors other Mississippi mud cake and brownie recipes where the eggs are thoroughly incorporated for a fudgy texture.
Sift or whisk in the 1/3 cup cocoa powder, 1 1/2 cups all-purpose flour, and 1/4 teaspoon salt until just combined, forming a thick brownie-like batter. Gently fold in the 1 cup chopped pecans.
Spread the batter evenly in the prepared 9×13 pan.
3. Bake the brownies
Bake for about 25–30 minutes, or until a toothpick inserted near the center comes out with a few moist crumbs but no raw batter. Mississippi mud-style bases are usually baked just until set so they stay moist and fudgy rather than cakey. Avoid overbaking, as the brownies will go back into the oven briefly with the marshmallows.
4. Add the marshmallow layer
Remove the pan from the oven and immediately sprinkle the 4 cups mini marshmallows evenly over the hot brownie surface. Return the pan to the oven for about 3–5 minutes, just until the marshmallows puff and begin to soften. They should be melty and pillowy but not deeply browned, similar to instructions in many Mississippi mud cake recipes.
Take the pan out and set it aside while you prepare the frosting.
5. Make the chocolate frosting
In a medium saucepan over medium heat, melt the 1/2 cup butter. Whisk in the 1/3 cup cocoa powder and 1/3 cup milk until smooth and just starting to steam; some versions bring this mixture to a brief boil, but gentle heating is enough as long as the cocoa is fully dissolved.
Remove the pan from heat and stir in the 1 teaspoon vanilla extract. Gradually whisk in the 3 1/2 cups powdered sugar, about a cup at a time, until the frosting is smooth, pourable, and thick but still spreadable. This method matches the pour-over icings used in Mississippi mud cakes, where the warm frosting flows over marshmallows and sets into a soft, fudgy layer.
If the frosting seems too thick to pour, add a splash more milk; if too thin, whisk in a bit more powdered sugar.
6. Frost the marshmallow-topped brownies
While the marshmallows are still warm and soft, pour or spoon the warm chocolate frosting evenly over the top, trying to cover as much of the surface as possible. Use an offset spatula to gently spread the frosting, being careful not to drag the marshmallows too aggressively. In many recipes, the frosting sinks slightly between the marshmallows, creating that signature “muddy,” swirled look.
You can optionally sprinkle extra chopped pecans over the frosted top for added crunch and a nod to traditional Mississippi mud cake presentations.
7. Cool, slice, and serve
Let the Mississippi Mud Cake Brownies cool completely at room temperature so the frosting sets and the layers firm up. This can take 1–2 hours or longer, depending on room temperature.
Once cool, cut into squares using a sharp knife. Wiping the knife between cuts will help you achieve neater edges through the marshmallow and frosting layers, a tip often given for mud cakes and marshmallow brownies.
Serve at room temperature. The brownies are rich, so smaller squares go a long way.
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