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Mississippi Mud Pie

Mississippi mud pie is a classic American dessert with a fudgy brownie base, a hot marshmallow layer, and a glossy chocolate ganache-style frosting topped with crushed walnuts. Bake the brownies, puff the marshmallows in the oven, then chill until clean slices set the fudgy texture.
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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: 430
Ingredients Equipment Method Notes

Ingredients
  

Fudgy brownie base
  • 1 cup unsalted butter
  • 2 cup sugar
  • 4 eggs
  • 2 tsp vanilla
  • 1.5 cup flour
  • 0.75 cup cocoa
  • 0.5 tsp salt
Marshmallow layer
  • 3 cup mini marshmallows
Chocolate frosting
  • 0.5 cup unsalted butter
  • 0.33 cup cocoa powder
  • 0.33 cup whole milk
  • 3 cup powdered sugar
  • 1 tsp vanilla
  • 1 cup walnuts or pecans

Equipment

  • 1 sheet pan

Method
 

Bake the fudgy brownie base
  1. Preheat oven to 350F and grease a 9x13 pan.
  2. Melt the butter and whisk in the sugar, eggs, and vanilla until glossy.
  3. Fold in the flour, cocoa, and salt until no dry streaks remain.
  4. Bake 25-28 minutes, until the center looks set rather than liquid.
Puff the marshmallow layer
  1. Immediately scatter the mini marshmallows over the hot brownies.
  2. Return to the oven for 3-4 minutes, until marshmallows are puffed and lightly golden.
Make and spread the chocolate frosting
  1. Melt the butter, then whisk in the cocoa and whole milk and heat just 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.
  4. Scatter the walnuts or pecans over the frosting surface.
Chill and cut
  1. Refrigerate for 2 hours before cutting, so the layers hold their shape.

Notes

For the cleanest slices, chill fully at least 2 hours, then cut with a warm knife (wipe between cuts). Store covered in the refrigerator up to 4 days; freeze baked, cut portions for up to 2 months. For a nut-free option, replace walnuts/pecans with toasted sunflower seeds for crunch.