Mississippi Mud Cake in a 9x13 Pan

Mississippi mud cake in a 9×13 pan is a dense chocolate cake made with 1 cup of melted butter, 2 cups of sugar, 4 eggs, 1 1/2 cups of flour, cocoa and pecans, baked at 350°F for 30 to 35 minutes. While it is still hot, it is covered with about 4 cups of mini marshmallows and then a pour-over chocolate frosting, so every square has three layers: fudgy cake, soft marshmallow and glossy icing.

It is a Southern potluck dessert meant to be served straight from the pan.

Why This Recipe Fits a 9×13 Pan

The marshmallow and frosting layers are poured over the cake while it is still in the pan, so the pan is the serving dish. A 9×13 gives a cake about 1 1/2 inches tall with room above it for the toppings without anything running over the sides. The pan also holds in the heat that melts the marshmallows.

Ingredients for a 9×13 Mississippi Mud Cake

Cake

1 cup (2 sticks) unsalted butter, melted
2 cups granulated sugar
1/3 cup unsweetened cocoa powder
4 large eggs
2 teaspoons vanilla extract
1 1/2 cups all-purpose flour
1/2 teaspoon salt
1 cup chopped pecans
4 cups mini marshmallows

Chocolate Frosting

1/2 cup (1 stick) unsalted butter
1/3 cup unsweetened cocoa powder
1/2 cup milk
4 cups (1 pound) powdered sugar
1 teaspoon vanilla extract

How to Make Mississippi Mud Cake in a 9×13 Pan

Heat the oven to 350°F and grease a 9×13 pan.
Mix the batter. Whisk the melted butter, sugar and cocoa. Whisk in the eggs and vanilla, then stir in the flour, salt and pecans.
Bake 30 to 35 minutes, until the center is set and a toothpick comes out with moist crumbs.

Add the marshmallows. Scatter the marshmallows over the hot cake and return it to the oven for 2 to 3 minutes, just until they puff and soften.
Make the frosting. Melt the butter with the cocoa and milk in a saucepan, then whisk in the powdered sugar and vanilla until smooth.
Pour and cool. Pour the warm frosting over the marshmallows and spread gently; some swirling is part of the look. Cool at least 2 hours before cutting.

Cook and Prep Times

Prep: 20 minutes
Bake: 30 to 35 minutes at 350°F, plus 2 to 3 minutes for the marshmallows
Cool: 2 hours
Serves: 20 to 24 squares

Cutting Clean Squares

Marshmallow sticks to everything. Let the cake set completely, then cut it with a long knife dipped in hot water and wiped dry between cuts. Chilling the cake for 30 minutes first also helps.

Changing the Pan Size

8×8 or 9×9 pan: halve everything (2 eggs) and bake 25 to 30 minutes.

Half-sheet pan: double the cake and bake 25 to 30 minutes; the frosting recipe as written still covers it thinly.

Storage

Cover the pan and keep it at room temperature for up to 3 days or in the refrigerator for up to a week. The marshmallow layer gets chewy in the cold, so let refrigerated squares sit out 20 minutes before eating.

Frequently Asked Questions

Can I leave out the pecans?

Yes. Leave them out of the cake, or put them on top of the frosting instead so guests can pick around them.

Is it the same as Texas sheet cake?

No. Texas sheet cake is a thin cake baked in a large sheet pan with a pour-over frosting and no marshmallows. Mud cake is thicker and denser.

For more bakes sized for the same pan, see our Texas sheet cake in a 9×13 pan, s’mores bars in a 9×13 pan and German chocolate cake in a 9×13 pan.

Mississippi Mud Cake in a 9×13 Pan