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Mississippi Mud Pie

Mississippi mud pie with a fudgy brownie base, a puffed marshmallow layer, and a glossy chocolate ganache-style frosting topped with crushed walnuts. Baked until the brownies are set, then marshmallows are toasted in the oven for a golden, cloud-like top before chilling into clean slices.
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Prep Time 25 minutes
Cook Time 40 minutes
Chilling 2 hours
Total Time 3 hours 5 minutes
Servings: 12 servings
Course: Dessert
Cuisine: American
Calories: 460
Ingredients Equipment Method Notes

Ingredients
  

Mississippi mud pie
  • 1 cup unsalted butter Plus more for greasing the pan if needed.
  • 2 cup sugar
  • 4 eggs
  • 2 tsp vanilla
  • 1.5 cup flour
  • 0.75 cup cocoa Unsweetened cocoa powder.
  • 0.5 tsp salt
  • 3 cup mini marshmallows For the marshmallow layer.
  • 0.5 cup unsalted butter For the chocolate frosting.
  • 0.33 cup cocoa powder For the chocolate frosting.
  • 0.33 cup whole milk
  • 3 cup powdered sugar
  • 1 tsp vanilla For the chocolate frosting.
  • 1 cup walnuts or pecans Roughly chopped; pressed into the ganache surface.

Equipment

  • 1 sheet pan
  • 1 oven

Method
 

Bake the fudgy brownie base
  1. Preheat the oven to 350F and grease a 9x13 pan with a thin layer of butter.
  2. Melt the unsalted butter, then whisk in the sugar, eggs, and vanilla until glossy and smooth.
  3. Fold in the flour, cocoa, and salt just until no dry streaks remain.
  4. Bake for 25-28 minutes, until the center is set and the top looks slightly dry.
  5. Immediately scatter the mini marshmallows over the hot brownies, then return to the oven for 3-4 minutes until puffed and golden.
Make the chocolate frosting and assemble
  1. For the frosting, melt the unsalted butter in a saucepan, then whisk in the cocoa powder and whole milk until smooth.
  2. Remove from heat, then whisk in the powdered sugar and vanilla until thick and pourable.
  3. Pour the warm frosting over the marshmallow layer, then scatter the chopped walnuts or pecans over the top.
Chill and serve
  1. Refrigerate for 2 hours before cutting so the layers firm up cleanly.

Notes

Pro tip: for the most fudgy brownie texture, avoid overbaking—pull the pan when the center is just set. Refrigerate covered up to 4 days; freeze the sliced pie up to 2 months (thaw in the fridge overnight). For a nut-free option, swap walnuts or pecans with toasted coconut or omit entirely.