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Mississippi mud cake is a Southern sheet cake with a reputation for being a mess, and every bit of the mess is deliberate. There is a dense, fudgy chocolate cake full of chopped pecans, a layer of miniature marshmallows melted onto the top, and a warm cocoa icing that runs into the marshmallows and sets into a chewy, sticky lid. It has been in the community cookbooks since the 1970s at least, and in family reunion coolers a good deal longer.
Everything that makes it work happens in about ten minutes, while the cake is hot. A cool cake will not melt the marshmallows, and unmelted marshmallows sit on top like a layer of pebbles. So the marshmallows go on the minute the pan comes out, the pan goes back in for 2 or 3 minutes, and the icing, made in a saucepan while the cake baked, goes on warm while the marshmallows are still soft. As it cools the two set together into one layer that pulls when you cut it. Whether to cut it warm is the household argument. Warm, the first square comes out in pieces, and that one is for the cook.
Why this Mississippi mud cake works
- Melted butter, not creamed. The batter is mixed like a brownie, so the cake bakes dense and fudgy rather than light.
- Marshmallows on the hot cake, 2 to 3 minutes back in the oven. The heat softens them just to the point of slumping, so they spread into a layer instead of sitting as lumps.
- A warm poured icing. A cooked cocoa icing poured while still hot spreads itself, melts into the marshmallows and sets glossy.
- Pecans in the cake. Toasted, chopped pecans give the dark cake its crunch and its Southern signature.
Ingredients
Makes one 9 by 13 inch sheet cake, 24 squares. The measurements are in US cups with grams in brackets.
For the cake
- 1 cup unsalted butter (2 sticks, 226g)
- 2 cups granulated sugar (400g)
- 1/3 cup unsweetened cocoa powder (30g)
- 4 large eggs
- 1 teaspoon vanilla extract
- 1 1/2 cups all-purpose flour (190g)
- 1/2 teaspoon fine salt
- 1 cup chopped pecans (115g)
- 1 cup sweetened flaked coconut (85g), optional
For the top
- 4 cups miniature marshmallows (200g, about half a 16 ounce bag)
For the icing
- 1/2 cup unsalted butter (113g)
- 1/3 cup unsweetened cocoa powder (30g)
- 1/3 cup whole milk (80ml)
- 3 1/2 cups powdered sugar (420g)
- 1 teaspoon vanilla extract
- 1/2 cup chopped pecans (57g), optional, for the top
Use natural unsweetened cocoa, the plain kind. Miniature marshmallows melt evenly; large ones do not soften in time. Toast the pecans 8 minutes at 350°F while the oven heats.
How to make Mississippi mud cake
The cake
- Heat the oven to 350°F (175°C). Grease a 9 by 13 inch metal baking pan.
- Melt the 1 cup butter in a large saucepan over low heat. Take it off the heat and whisk in the sugar and the 1/3 cup cocoa until smooth and glossy.
- Whisk in the eggs one at a time, then the vanilla. Add the flour and salt and stir with a spatula just until no dry streaks remain. Fold in the pecans and the coconut, if using. The batter is thick, like brownie batter.
- Spread it evenly in the pan. Bake at 350°F for 30 to 35 minutes, until the top is set and dull and a toothpick in the center comes out with moist crumbs, not wet batter. Do not overbake; this is a fudgy cake.
The marshmallows and the icing
- While the cake bakes, make the icing. Melt the 1/2 cup butter in a medium saucepan, whisk in the 1/3 cup cocoa and the milk, and bring just to a boil, stirring. Take it off the heat and whisk in the powdered sugar a cup at a time, then the vanilla, until smooth and pourable. Keep it warm over the lowest heat. If it thickens, whisk in a tablespoon of hot milk.
- The moment the cake comes out, scatter the marshmallows evenly over the hot top. Return the pan to the oven for 2 to 3 minutes, just until the marshmallows puff and start to slump and melt into one another. Do not let them brown.
- Take the pan out and immediately pour the warm icing over the marshmallows in wide ribbons. Use a knife to nudge it into the corners and drag a few light swirls through the marshmallow so the white and brown run together. Do not try to smooth it. Scatter the extra pecans on top if you like.
- Cool in the pan on a rack for at least 1 hour, so the top sets into a chewy layer. Cut into 24 squares in the pan.
Tips that make the difference
- Have the icing made and warm before the cake comes out. Ten minutes of hunting for the powdered sugar is ten minutes of the cake cooling.
- Two to three minutes for the marshmallows, no more. Past the slump they brown and toughen into a skin.
- Pour the icing, do not spread it. Pushing a spatula through half-melted marshmallow drags it into the icing and makes grey streaks.
- Cut with a hot, wet knife, wiped between cuts, and the squares come out clean instead of stringy.
Variations
- Peanut butter mud cake. Swap the pecans for chopped roasted peanuts and whisk 1/4 cup creamy peanut butter (65g) into the warm icing.
- Without nuts. Leave the pecans out and keep the coconut, or fold 1 cup miniature chocolate chips (170g) into the batter.
- Marshmallow creme. Spread 7 ounces of marshmallow creme (200g) over the hot cake in place of the miniatures and go straight to the icing.
- Cupcakes. Fill 24 lined muffin cups two thirds full, bake 18 to 20 minutes, top each with 6 or 7 marshmallows, 2 minutes back in the oven, then a spoonful of warm icing.
Storage and make-ahead
Covered in the pan at room temperature, the cake keeps 4 days. The top stays chewy and the cake underneath stays fudgy.
It travels well. Cut it in the pan, cover it with foil, and it is the cake that goes to the potluck and the family reunion, because nothing about it can be ruined in a car.
Squares freeze for up to 2 months, wrapped individually. The marshmallow layer gets a little chewier after thawing.
Frequently asked questions
Why do the marshmallows go on the hot cake?
Because the heat of the cake, plus 2 to 3 minutes back in the oven, is what melts them into a soft layer. On a cool cake they stay whole and the icing sits on top of them like a lid on a pile of pebbles.
Can I frost it after it cools?
You can, and it will taste fine, but you will have a plain frosted chocolate cake with marshmallows in the way. The swirled, chewy, run-together top only happens when everything is warm at once.
Why is my icing grainy?
The powdered sugar went into the pan while it was still boiling, or it was not whisked in fully. Take the pan off the heat before adding the sugar, and if it seizes, whisk in hot milk a tablespoon at a time.
Is Mississippi mud cake the same as Mississippi mud pie?
No. The pie is a chocolate pudding or brownie filling in a cookie crust, served cold. The cake is a baked chocolate pecan sheet cake with a marshmallow and cocoa icing top. They share a name and a color and not much else.
Bake it fudgy, cover it with marshmallows while it steams, pour the icing on warm, and let the mess set for an hour if you can stand to. The first square is still for the cook.
Mississippi Mud Cake (Marshmallows on the Hot Cake)
The old-fashioned Mississippi mud cake: a chocolate pecan sheet cake in a 9 by 13 pan, miniature marshmallows melted on the hot cake for 2 to 3 minutes in the oven, then a warm cocoa icing poured over the whole thing. Cups and grams.
Ingredients
- 1 cup unsalted butter
- 2 cups granulated sugar
- 1/3 cup unsweetened cocoa powder
- 4 large eggs
- 1 teaspoon vanilla extract
- 1 1/2 cups all-purpose flour
- 1/2 teaspoon fine salt
- 1 cup chopped pecans
- 1 cup sweetened flaked coconut (85g), optional
- 4 cups miniature marshmallows
- 1/2 cup unsalted butter
- 1/3 cup unsweetened cocoa powder
- 1/3 cup whole milk
- 3 1/2 cups powdered sugar
- 1 teaspoon vanilla extract
- 1/2 cup chopped pecans (57g), optional, for the top
Instructions
- Heat the oven to 350°F (175°C). Grease a 9 by 13 inch metal baking pan.
- Melt the 1 cup butter in a large saucepan over low heat. Take it off the heat and whisk in the sugar and the 1/3 cup cocoa until smooth and glossy.
- Whisk in the eggs one at a time, then the vanilla. Add the flour and salt and stir with a spatula just until no dry streaks remain. Fold in the pecans and the coconut, if using. The batter is thick, like brownie batter.
- Spread it evenly in the pan. Bake at 350°F for 30 to 35 minutes, until the top is set and dull and a toothpick in the center comes out with moist crumbs, not wet batter. Do not overbake; this is a fudgy cake.
- While the cake bakes, make the icing. Melt the 1/2 cup butter in a medium saucepan, whisk in the 1/3 cup cocoa and the milk, and bring just to a boil, stirring. Take it off the heat and whisk in the powdered sugar a cup at a time, then the vanilla, until smooth and pourable. Keep it warm over the lowest heat. If it thickens, whisk in a tablespoon of hot milk.
- The moment the cake comes out, scatter the marshmallows evenly over the hot top. Return the pan to the oven for 2 to 3 minutes, just until the marshmallows puff and start to slump and melt into one another. Do not let them brown.
- Take the pan out and immediately pour the warm icing over the marshmallows in wide ribbons. Use a knife to nudge it into the corners and drag a few light swirls through the marshmallow so the white and brown run together. Do not try to smooth it. Scatter the extra pecans on top if you like.
- Cool in the pan on a rack for at least 1 hour, so the top sets into a chewy layer. Cut into 24 squares in the pan.
