Mississippi Mud Brownies

These Mississippi Mud Brownies are the definition of chocolate overload, in the best way possible. You’ve got a fudgey brownie base, gooey marshmallows melted right on top, and a rich chocolate frosting to seal the deal. They’re messy, indulgent, and impossible to resist…a little bit like Tim Riggins. Make sure to let them cool completely before cutting so you get those perfect, stacked layers in every bite. I firmly believe when coupled with a Diet Coke, they form the New Breakfast of Champions.

Ingredients & Equipment Needed

Brownies:
- all-purpose flour
- sugar
- unsweetened cocoa powder
- baking powder
- salt
- butter
- eggs
- vanilla extract
- dark or semi-sweet chocolate chips or chunks
- mini marshmallows or flat marshmallows
Frosting:
- butter
- unsweetened cocoa powder
- evaporated milk or whole milk
- powdered sugar
- vanilla
9×13 baking dish

How to Make Mississippi Mud Brownies

This is a simple overview of the recipe, you’ll find a full printable recipe below!

Preheat oven to 350°F and prep a 9×13 pan.
Mix dry ingredients, then add melted butter, eggs, and vanilla; beat until smooth. Stir in chocolate chips and spread batter in pan.
Bake until set (time varies greatly, but definitely start checking early).
Top with marshmallows, return briefly to oven until puffed, then cool completely.
Whip frosting until fluffy, spread over cooled brownies, and slice into squares.

A Note About Baking Time & Other Tips

Baking time: there is a bit of debate about how long these need to bake. Unfortunately, I don’t have a perfect answer, and there are a lot of variables. Here are the facts:
- These brownies should be moist and fudgy.
- The original recipe says to bake them for 30 minutes.
- I am essentially at sea-level and bake these in a glass Pyrex 9×13 pan.
- At 25 minutes (because I always recommend checking a few minutes before they’re supposed to be done), my brownies were just starting to firm up around the very, very edges of the pan and were completely liquid inside.
- I checked them every five minutes and they were done in the 45 – 50 minute range.
- Other people have had them come out dry at 30 – 35 minutes.
- If you’re baking them in a metal pan, they’ll take less time, especially if it’s a dark metal pan.
- Usually things at a low elevation bake faster, but apparently not in this case.
- Bottom line: start checking on them around 25 – 30 minutes and keep checking every 5 until the toothpick just barely comes out clean.
Cutting: these can be kind of a pain to cut, especially getting the first few out, but just take your time and make firm, straight-down cuts (to make sure the marshmallows are getting cut), wiping the blade often. A plastic knife (just the disposable kind) actually works better than just about anything else.

Frequently Asked Questions

Baking times vary a lot. How do I know when the brownies are done?

Watch for lightly set edges and a slightly soft center. A toothpick inserted in the middle should come out with a few moist crumbs.

Do I need to let them cool completely before frosting and cutting?

Yes, letting them cool totally (including the marshmallow layer) helps the frosting set better and gives cleaner slices.

Can I use a different size or type of baking pan?

You can, just note that using a thinner or metal pan may change the bake time. Dark metal pans bake faster, and using a larger pan will thin out the layers.

What marshmallows work best? Big? Thin? Mini?

I love the flat marshmallows for this recipe, but mini works great too. Just cover the surface well, so they distribute and melt evenly.

Can I use a boxed brownie mix instead of making them from scratch?

Totally! Just adjust the baking time as needed and ensure brownies are baked long enough to support the marshmallow and frosting layers without becoming soggy.

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