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Mississippi Mud Pie

Mississippi mud pie layers a fudgy brownie base with a marshmallow blanket, then tops everything with glossy chocolate ganache-style frosting and crunchy walnuts. Baked until just set, puffed marshmallows finish the texture, while the chilled slice holds clean, fudgy edges.
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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
  

For fudgy brownie base
  • 1 cup unsalted butter
  • 2 sugar
  • 4 eggs
  • 2 tsp vanilla
  • 1.5 cup flour
  • 0.75 cup cocoa
  • 0.5 tsp salt
For marshmallow layer
  • 3 cup mini marshmallows
For chocolate frosting
  • 0.5 cup unsalted butter
  • 0.333 cup cocoa powder
  • 0.333 cup whole milk
  • 3 cup powdered sugar
  • 1 tsp vanilla
  • 1 cup walnuts or pecans, roughly chopped

Equipment

  • 1 sheet pan

Method
 

Bake the fudgy brownie base
  1. Preheat oven to 350°F, then grease a 9x13 pan.
  2. Melt the unsalted butter and whisk in the sugar, eggs, and vanilla until smooth.
  3. Fold in the flour, cocoa, and salt just until combined, then spread batter into the prepared pan.
  4. Bake 25-28 minutes, until the center looks set but still fudgy.
Add marshmallow layer
  1. Immediately scatter mini marshmallows over the hot brownies in an even layer.
  2. Return the pan to the oven for 3-4 minutes, until marshmallows puff and turn lightly golden.
Make chocolate frosting and assemble
  1. Melt the butter, then whisk in cocoa powder and whole milk until smooth.
  2. Remove frosting from the heat and whisk in powdered sugar and vanilla until glossy.
  3. Pour warm frosting over the marshmallow layer, then scatter walnuts or pecans over the surface.
Chill and slice
  1. Refrigerate for 2 hours before cutting, so the ganache firms up for clean slices.

Notes

Pro tip: bake until the brownie is set but not dry, because it continues to firm as the marshmallows puff and the frosting cools. Store leftovers covered in the refrigerator for up to 4 days; freeze slices in an airtight container for up to 2 months. For a lighter option, use mini marshmallows labeled “reduced sugar” and swap half the powdered sugar for a no-sugar-added frosting blend (texture will be slightly less rich).