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Mississippi Mud Cake
This one-pan Mississippi mud cake is pure indulgence with rich chocolate cake topped with gooey marshmallows and a warm, fudgy frosting. Perfect for potlucks, parties, or anytime you want a crowd-pleasing dessert with big nostalgic flavor.
Ingredients
For the cake:
- 1 cup (226 g) unsalted butter
- 1/3 cup (28 g) unsweetened cocoa powder
- 1 cup (240 ml) water
- 2 cups (400 g) granulated sugar
- 2 cups (240 g) all-purpose flour
- 1/2 teaspoon salt
- 1 teaspoon baking soda
- 2 large eggs, at room temperature
- 1/2 cup (120 ml) buttermilk, at room temperature
- 1 teaspoon vanilla extract
For the topping and frosting:
- 3 to 4 cups mini marshmallows, enough to mostly cover the cake
- 1/2 cup (113 g) unsalted butter
- 1/4 cup (21 g) unsweetened cocoa powder
- 1/3 cup (80 ml) milk
- 3 to 3 1/2 cups (330 to 385 g) confectioners’ sugar, sifted
- 1 teaspoon vanilla extract
- 3/4 to 1 cup chopped pecans or walnuts, optional
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Instructions
To make the cake:
- Preheat oven to 350°F (175°C). Grease a 9x13-inch pan.
- In a medium saucepan, melt the butter with the cocoa powder and water over medium heat. Bring just to a boil, then remove from the heat. Let the cocoa mixture cool for about 5 minutes before adding to the dry ingredients. This helps prevent the eggs from cooking when added.
- In a large bowl, whisk together the sugar, flour, salt, and baking soda. Pour in the hot cocoa mixture and stir to combine.
- Add the eggs, buttermilk, and vanilla, stirring just until smooth.
- Pour the batter into the prepared pan and bake for 25–30 minutes, or until a toothpick comes out with a few moist crumbs.
To make the topping and frosting:
- As soon as the cake comes out of the oven, scatter the mini marshmallows evenly over the top. Return to the oven for 2–3 minutes, just until the marshmallows puff and soften. Cool briefly on a wire rack while you make the frosting.
- In a saucepan, melt the butter with the cocoa powder and milk. Remove from the heat and whisk in the confectioners’ sugar, vanilla, and nuts if using.
- While the frosting is still warm and the marshmallows are soft, pour or spoon the frosting evenly over the top of the warm cake. Gently spread as needed to cover, but don’t press or swirl. Try to keep the marshmallow layer intact.
- Let the cake cool completely before slicing. It cuts best once set.
Notes
- Let the cocoa mixture cool for about 5 minutes before adding to the dry ingredients to avoid scrambling the eggs.
- Pour the frosting over the marshmallows while both are still warm for the best texture and distinct layers. Don’t worry about completely covering every bit of marshmallow. It’s better to have a few puffy marshmallow peaks showing through than to overwork the top and lose that soft, gooey layer. I find that trying to cover as much of the cake while pouring works best because spreading it afterwards is a challenge.
- Store covered at room temperature for 2 days or in the refrigerator for up to 5 days. Freeze for up to 2 months.
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