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Mississippi Mud Pie

Mississippi mud pie with a fudgy brownie base, marshmallow layer, and glossy chocolate frosting. The marshmallows puff after a quick bake step, then the whole dessert chills for clean, sliceable squares.
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Prep Time 25 minutes
Cook Time 40 minutes
chilling 2 hours
Total Time 4 hours 45 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
  • 0.333 cup cocoa powder
  • 0.333 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 so the brownie releases cleanly.
  2. Melt the unsalted butter and whisk in the sugar, then whisk in the eggs and vanilla until glossy and smooth.
  3. Fold in the flour, cocoa, and salt just until the batter is combined with no dry streaks.
  4. Bake 25-28 minutes at 350F until the brownie is set around the edges but still fudgy in the center (a toothpick should come out with moist crumbs).
Puff the marshmallow layer
  1. Immediately scatter the mini marshmallows over the hot brownies so they start melting right away.
  2. Return to the oven for 3-4 minutes at 350F until the marshmallows puff and turn lightly golden on top.
Make frosting and finish
  1. Melt the unsalted butter, then whisk in the cocoa powder and whole milk and remove from heat.
  2. Whisk in the powdered sugar and vanilla until the frosting is smooth and thick enough to pour.
  3. Pour the warm frosting over the marshmallow layer, covering it evenly for a glossy top.
  4. Scatter walnuts or pecans over the frosting and press them in lightly so they adhere.
  5. Refrigerate for 2 hours to set the frosting fully before cutting into squares.

Notes

For the cleanest slices, chill the pie until the frosting feels firm to the touch, then wipe your knife between cuts. Store covered in the refrigerator up to 4 days; freeze slices for up to 2 months (thaw overnight in the fridge). For a lighter option, use a reduced-sugar chocolate frosting substitute for part of the powdered sugar, keeping the rest to maintain the set.