★★★★★

Marshmallow Brownies

Two classic treats come together in Marshmallow Brownies. Fudgy brownies are covered in a gooey marshmallow topping. This decadent dessert keeps everyone coming back for more!

If you love marshmallows and chocolate, you’ll flip for my Rocky Road Fudge and S’mores Cookie Bars too. But today it’s all about the brownies!

Brownies with a layer of marshmallow and chocolate icing with a bite taken out.

Mississippi Mud Brownies

My affinity for baking with marshmallows is well documented on this blog. So is my devotion to brownies.

This Marshmallow Brownies recipe brings these two great loves together at long last.

  • Similar to the decadence of Mississippi Mud cake, these brownies are covered in a rich chocolate frosting and lots of marshmallows.
  • Made with buttermilk, the icing soaks into the brownies making them extra moist.

If you want a marshmallow brownies recipe that’ll blow everyone away, look no further. These are ooey-gooey, chocolate-y, fudgy, totally over-the-top brownies that no one can resist.

Don’t forget the cream cheese swirls. Our cheesecake brownies need to be up next on your baking to-do list!

Ingredient Notes

Ingredients needed to make marshmallow topped brownies.

We started by making our favorite thick and fudgy brownie recipe. You’ll see these featured on our website from frosted brownies to oreo brownies, and every flavor in between. We use them as a base because there truly is no better recipe!

  • Buttermilk. You can use store bought or my Buttermilk Substitute.
  • Cocoa powder. Use a good quality unsweetened cocoa for best results.
  • Mini marshmallows. Make sure your marshmallows are fresh! Or use our homemade marshmallows instead!
  • Vanilla extract. A high quality extract like this homemade Vanilla Extract yields the richest flavor.
Step by step photos showing how to make marshmallow brownies.

Easy Instructions

Make the brownies. Unlike our basic brownie, these will be made in a 13×9 dish. Because of the marshmallow and frosting, they’ll still be super thick!

Add Marshmallows. Sprinkle marshmallows all over the top of the warm brownies. Put the pan of marshmallows bake in oven for a few seconds. Remove when the marshmallows begin to puff up.

PRO TIP: Be sure to use FRESH mallows. If you’re using stale or old marshmallows, they’ll still taste stale.

Add chocolate icing. Pour the warm frosting over the cooled brownies. Let the brownies set and cool before slicing.

Chocolate brownie with marshmallow being broken in half on a plate.

Tips and Tricks

  • DO NOT OVER MIX. When adding the dry ingredients, mix them in until just combined. You shouldn’t see any flour visible but a few small lumps in the batter are okay. Over mixing will make your brownies cakey instead of fudgy.
  • Frosting sets quickly, so be sure to pour it over the brownies fast.
  • How to slice brownies. Use a plastic knife to easily cut marshmallow brownies into squares. It works better than a metal knife. Clean slices with no tearing!
  • Storing. Transfer cooled brownies to an airtight container. They keep well for up to 4 days.
  • Chill. I prefer these brownies served COLD. Keep in the fridge if you like the taste of chilled brownies too!
  • Reheat brownies for a gooey marshmallow filling by popping them in the microwave for about 10 seconds.
Slice of brownie with marshmallow and chocolate icing.

Recipe FAQs

Can you freeze Mississippi Mud Brownies?

Yes, marshmallow brownies can be frozen. Transfer cut brownies to freezer bags and store frozen for up to 3 months. Freeze before or after adding the frosting. Your choice!

I don’t have buttermilk. Can I still make these brownies?

Yes, you can make the marshmallow brownies recipe with Homemade Buttermilk. I’ve made it with both homemade and store bought with equally good results.

What kind of dish do I need to bake these?

I used a 13 x 9 baking pan to make these brownies. You can make them in a square brownie pan instead but the brownies will be much thicker and need more baking time.

More Brownies, Bars, and Cookies

Yield: 24 brownies

Marshmallow Brownies Recipe

Prep Time 10 minutes
Cook Time 24 minutes
Total Time 34 minutes

Two classic treats come together in Marshmallow Brownies. Fudgy brownies are covered in a gooey marshmallow topping. This decadent dessert keeps everyone coming back for more!

Ingredients

For the Brownies

  • 1 cup unsalted butter
  • ½ cup semi-sweet chocolate morsels
  • 2 cups granulated sugar
  • 4 large eggs
  • 1 teaspoon vanilla extract
  • ¾ cup unsweetened cocoa powder
  • 1 cup all-purpose flour
  • ½ teaspoon kosher salt
  • ½ teaspoon baking powder

For the topping

  • 4 cups mini marshmallows
  • ½ cup unsalted butter
  • ½ cup buttermilk
  • ¼ cup unsweetened cocoa powder
  • 4 cups powdered sugar

Instructions

For the Brownies

  1. Preheat oven to 350°F. Line a 13x9 baking dish with parchment paper. Set aside.
  2. In a medium sized saucepan, melt butter over medium heat. Remove from heat and add in chocolate chips and sugar.
  3. Stir until chocolate is completely melted. Add in eggs, one at a time, stirring completely after each addition. Stir in vanilla.
  4. Add the cocoa powder, flour, salt, and baking powder. Using big strokes, stir in JUST until mixed and no longer see dry ingredients. DO NOT BEAT OR OVER STIR.
  5. Pour batter into dish and bake for about 22-24 minutes. Remove from oven and sprinkle with mini marshmallows.
  6. Place pan back in oven and bake for 90 seconds, until marshmallows puff in size. Remove from oven and cool.

For the Topping

  1. In a small saucepan, melt butter over medium heat. Once melted, whisk in the buttermilk and cocoa powder.
  2. Keep whisking until mixture begins to boil, then remove from heat.
  3. In a large mixing bowl, add powdered sugar. Pour chocolate mixture in the bowl and using the whisk attachment, beat mixture until fully combined and smooth. This will take several minutes, you don't want the sugar grainy.
  4. Pour warm frosting over brownies (it's okay if the brownies aren't completely cooled yet).
  5. Let set and cool, completely.

Notes

  • DO NOT OVER MIX. When adding the dry ingredients, mix them in until just combined. You shouldn't see any flour visible but a few small lumps in the batter are okay. Over mixing will make your brownies cakey instead of fudgy.
  • Frosting sets quickly, so be sure to pour it over the brownies fast.
  • How to slice brownies. Use a plastic knife to easily cut marshmallow brownies into squares. It works better than a metal knife. Clean slices with no tearing!
  • Storing. Transfer cooled brownies to an airtight container. They keep well for up to 4 days.
  • Chill. I prefer these brownies served COLD. Keep in the fridge if you like the taste of chilled brownies too!
  • Reheat brownies for a gooey marshmallow filling by popping them in the microwave for about 10 seconds.
  • No Buttermilk? Use my easy buttermilk substitute, or swap it out completely and use whole milk.
  • See blog post for more recipe tips and tricks.
  • Nutrition Information:

    Yield:

    24

    Serving Size:

    1 brownie

    Amount Per Serving: Calories: 329Total Fat: 14gSaturated Fat: 8gTrans Fat: 0gUnsaturated Fat: 5gCholesterol: 62mgSodium: 67mgCarbohydrates: 50gFiber: 1gSugar: 42gProtein: 3g

    *Nutrition facts are an estimate and not guaranteed to be accurate. Please see a registered dietitian for special diet advice.

    Did you make this recipe?

    Please leave a comment on the blog or share a photo on Instagram

    Love Mississippi Mud Pie? These Marshmallow Brownies might just become your new favorite!

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    About Aimee

    Aimee is a dessert lover (specifically rice krispie treats), workout enthusiast, self-taught foodie, and recipe creator.

    Learn more about Aimee.

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    Posted on March 21, 2022

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