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Mississippi Mud Pie

Mississippi mud pie with a fudgy brownie base, melty marshmallow layer, and glossy chocolate ganache-style frosting topped with crushed walnuts. Baked until the marshmallows are puffed and golden, then chilled for clean, sliceable squares.
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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: 520
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 butter, then whisk in sugar, eggs, and vanilla until smooth.
  3. Fold in flour, cocoa, and salt just until no dry streaks remain.
  4. Spread batter into the greased pan and bake for 25-28 minutes, until the center looks set.
Add the marshmallow layer
  1. Immediately scatter mini marshmallows over the hot brownies.
  2. Return to the oven for 3-4 minutes, until marshmallows are puffed and golden.
Make and pour the chocolate frosting
  1. Melt butter for the frosting, then whisk in cocoa powder and whole milk and remove from heat.
  2. Whisk in powdered sugar and vanilla until the frosting is smooth.
  3. Pour warm frosting over the marshmallow layer, then scatter walnuts or pecans over the top.
Chill and slice
  1. Refrigerate for 2 hours, until firm enough to cut clean slices.

Notes

For the neatest slices, chill until fully firm; if it’s still soft after 2 hours, give it another 30 minutes in the fridge. Store covered in the refrigerator up to 4 days. Freeze slices in a sealed container up to 2 months. If you need a gluten-free version, swap in a 1:1 gluten-free baking flour blend for the flour.