
This marshmallow brownie recipe transforms a simple boxed mix into a gooey, decadent treat that everyone will fight over. The melty marshmallow middle layer creates that perfect sweet chewiness while the chocolate frosting brings everything together into dessert perfection.
I first made these brownies for my daughter's sleepover party and they disappeared within minutes. Now they're requested at every family gathering and I always come home with an empty pan.
Ingredients
- Brownie mix plus ingredients on box: Creates the perfect fudgy base saving you time while ensuring consistent results
- Mini marshmallows: Provide that classic gooey layer that gets puffy and slightly toasted for texture contrast
- Salted butter: In the frosting balances the sweetness with a subtle richness
- Unsweetened cocoa powder: Delivers deep chocolate flavor without making the frosting overly sweet
- Vanilla extract: Enhances all the chocolate notes with its aromatic warmth
Step-by-Step Instructions
- Prepare the Pan:
- Select the right baking dish based on your desired brownie thickness. For decadent thick brownies use a 9x9 inch pan which creates substantial squares. For thinner brownies that feed more people use a 9x13 inch pan. Ensure even brownie removal by either spraying thoroughly with nonstick spray or lining with parchment paper with overhang for easy lifting.
- Mix the Brownies:
- Follow the package directions exactly measuring oil water and eggs as specified. Mix until just combined about 50 strokes as overmixing can create tough brownies. The batter should look glossy and smooth with no dry pockets of mix remaining. Pour into your prepared pan spreading to the corners for even baking.
- Bake the Base:
- Place in preheated 350°F oven on the center rack for optimal heat distribution. Bake for 30 minutes until nearly done. Look for the edges to just begin pulling away from the sides but the center should still be slightly soft when tested with a toothpick. This slight underbaking ensures your final brownies will be fudgy rather than dry.
- Add Marshmallow Layer:
- Remove brownies from oven while still hot and immediately cover the entire surface with mini marshmallows creating an even layer. Make sure to spread them right to the edges for complete coverage. Return to the oven for just 3 minutes which allows them to puff up without becoming overly browned or melting completely away.
- Create the Frosting:
- In a large bowl combine softened butter powdered sugar cocoa powder milk and vanilla. The butter must be softened but not melted for the proper texture. Beat with electric mixer starting on low speed then increasing to medium until completely smooth with no lumps. Adjust consistency by adding tiny amounts of milk or powdered sugar until it reaches a spreadable but not runny consistency.
- Apply the Topping:
- Wait until the marshmallow layer has completely cooled before adding frosting otherwise it will melt into the marshmallows. Place spoonfuls of frosting across the surface then use a gentle touch with an offset spatula to spread without tearing the marshmallows beneath. Work from the center outward with light pressure for the best results.

I discovered the magic of using a plastic knife for cutting these brownies after ruining a batch with a regular knife. The marshmallow layer simply slides off the plastic rather than sticking making perfect squares possible even with such sticky ingredients.
Storage Tips
These brownies stay fresh at room temperature in an airtight container for up to 3 days. The marshmallow layer absorbs moisture from the air so proper storage is essential to maintain texture. For longer storage refrigerate for up to a week though the marshmallows will firm up slightly when cold. Allow refrigerated brownies to come to room temperature before serving for the best texture experience.
Creative Variations
Transform these brownies into rocky road style by adding 1 cup chopped walnuts or pecans to the brownie batter before baking. The nuts provide delightful crunch against the soft marshmallow. For a peanut butter lover's dream swirl 1/4 cup warmed peanut butter into the frosting before spreading. Another delicious option is sprinkling 1/2 cup shredded coconut over the marshmallows before the final baking for a tropical twist.

Serving Suggestions
These brownies make an extraordinary dessert when slightly warmed and topped with vanilla ice cream. The contrast between cold ice cream and the warm brownie creates a restaurant worthy experience. For special occasions arrange brownie squares on a platter drizzled with caramel sauce and a light dusting of sea salt. They also pack beautifully in lunch boxes or picnic baskets for treats on the go.
Frequently Asked Questions
- → Can I use homemade brownie batter instead of boxed mix?
Yes, you can substitute the boxed mix with your favorite homemade brownie recipe. Ensure the batter yield is similar to an 18-ounce box mix for best results.
- → How do I prevent overbaking the brownies?
Keep a close eye on the brownies during their initial bake. Remove them from the oven when they are just set and no longer jiggly, as they'll continue to cook slightly in residual heat.
- → Can I double the frosting recipe?
Absolutely! If you prefer a thicker layer of frosting, simply double the frosting ingredients. This works particularly well for thinner brownies baked in a 9x13 pan.
- → How should I store the brownies?
Store the brownies in an airtight container at room temperature for up to 3 days, or refrigerate for up to a week for prolonged freshness.
- → Can I add extra toppings?
Yes! Chopped nuts, sprinkles, or a drizzle of caramel or chocolate sauce make excellent toppings to customize your brownies.