Decadent marshmallow brownies have a fudgy brownie base topped with gooey marshmallows and chocolate frosting. A rich and easy dessert made with box mix!
Marshmallow Brownies with Box Mix
If you are a fan of my s’mores bars, then this dessert is for you! It’s the ultimate indulgence and is made with double chocolate and fluffy marshmallows.
I remember having these marshmallow brownies (also known as Mississippi mud brownies) growing up at a friend’s house. It was love at first bite from the rich fudge brownie base to the gooey marshmallow topping and chocolate buttercream frosting!
Ingredient Notes
- Boxed brownie mix: For the base, I prefer to save time and make marshmallow brownies using box mix. You can make my homemade brownie recipe if you prefer.
- Marshmallow layer: Mini marshmallows make up the 2nd layers and are puffy and gooey. Optionally, top with homemade marshmallow fluff and skip cooking.
- Chocolate frosting layer: Last, these are topped with a chocolate buttercream made with butter, powdered sugar, cocoa powder, milk and vanilla.
How to Make Marshmallow Brownies
Find the full printable recipe with specific measurements below.
- Brownies. Prepare the brownie mix according to the package directions. These are going to be fudgy chocolate brownies that are soft and moist. Mix the brownies with water, oil, and large eggs according to the box package.
- Bake. Pour the brownie batter mixture into a greased 9×9 inch pan and bake for 30 minutes, or until almost done.
- Mix. Beat the frosting ingredients in a large bowl with an electric mixer until smooth and creamy. You can use a whisk too.
- Marshmallows. Remove the brownies from the stove, then evenly sprinkle the mini marshmallows on top. Bake for about 3 minutes, or until the marshmallows have puffed up. Remove from oven and let cool.
- Spread. Place a few spoonfuls of the frosting on top of the marshmallow layer and spread with a spatula.
- Slice and serve. I like to cut the brownies in 5×4 rows with a plastic knife. Make them as big or as little as you need.
Baking Tips
Follow these helpful baking tips to make the best marshmallow brownies!
- Line pan. I like to line my pan with parchment paper and lightly grease it to prevent the marshmallows from getting stuck to the pan.
- Thick or thin. Use a 9×9″ baking dish for thicker brownies and a 9×13 inch baking dish for thinner brownies.
- Extra marshmallows. If using a 9×13″ pan, I’d recommend adding an extra cup of marshmallows and doubling the frosting.
- Chocolate lovers. Next, add 1/2 cup dark or milk chocolate chips to the brownie batter for even more chocolate flavor.
- Slicing. Use a plastic knife to easily cut the brownies and wipe them clean after each cut. Make sure they’ve cooled for about 30 minutes before cutting.
- Don’t overbake! The brownies should be gooey and fudgy. I use the toothpick method to check if they’re done. Stick a toothpick in the center of the brownies and it should come out clean.
Storing
- Store: These marshmallow brownies are simple to store. Place in an airtight container and store at room temperature or in the refrigerator. Enjoy within the week!
- Freeze: You can freeze marshmallow brownies in an airtight container for up to two months in the freezer.
More brownie recipes to make include homemade cosmic brownies, chocolate mint brownies and Oreo brownies.
More Brownie Recipes
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Marshmallow Brownie Recipe
Ingredients
- 18 ounce box brownie mix , plus ingredients on box
- 2 cups mini marshmallows , more if needed
Chocolate frosting:
- ¼ cup salted butter , softened
- 1 ½ cups powdered sugar
- 2 Tablespoons unsweetened cocoa powder
- 2 Tablespoons milk , more as needed
- ½ teaspoon vanilla extract
Instructions
Make the brownies:
- Preheat the oven to 350ºF. For thick brownies, spray a 9×9" pan with non-stick spray or line with parchment paper. If you'd like to make thinner brownies, use a 9×13" pan.
- Prepare the brownie mix according to the package directions. Then pour batter into the prepared pan. Bake for 30 minutes, or until almost done. Do not overcook. Remove from oven and then sprinkle 2 cups mini marshmallows over the top so that they are covering the brownies in an even layer. Bake an additional 3 minutes, or until the marshmallows have puffed up. Remove from oven and allow to cool.
Make the frosting:
- Combine 1/4 cup salted butter, 1 1/2 cups powdered sugar, 2 Tablespoons cocoa powder, 2 Tablespoons milk and 1/2 teaspoon vanilla in a large bowl. Beat with electric beaters until smooth. Add more milk or powdered sugar if needed to reach a smooth and creamy frosting. Then place spoonfuls on top of the marshmallows once cooled. Gently spread evenly.
- I like to cut the brownies in 5×4 rows with a plastic knife.
Notes
Nutrition
Nutrition provided is an estimate. It will vary based on specific ingredients used.
Did you make this recipe? Don’t forget to give it a star rating below!
Jamielyn Nye is the founder and recipe creator at I Heart Naptime. She is the author of the I Heart Naptime Cookbook and shares easy family-friendly recipes and desserts for every occasion.
Yummy. I used my homemade mint chocolate chip marshmallows.
Wow, that sounds delicious!