Fudgy brownies + crunchy PB + marshmallow fudge frosting = the best brownies on the planet. You should definitely make these peanut butter marshmallow fudge brownies ASAP!

Well, last week, I gave you the best, and maybe only, side dish recipe you’ll need this summer. I can’t believe all of you who made it in the last week and reported back here and on Instagram already. You guys are the best. Seriously.

Today, I’m going to do you another solid and give you the only dessert recipe you’re going to need this summer. Trust me. Neighborhood BBQs, church potlucks, Thursday afternoon coping skills. There is no event or reason wherein these peanut butter marshmallow fudge brownies would not be acceptable. 

Also, I couldn’t decide when to tell you this, but here goes: these brownies are shockingly good chilled (or frozen). Like, dangerously so. If your love language (and/or downfall) is peanut butter + chocolate, you’re either going to really love me or really hate me today.

What is marshmallow fudge frosting? 

Gosh, I’m glad you asked. There’s truly nothing I want to talk about more right now than marshmallow fudge frosting. Gloriously shiny. Just a little teeny bit chewy. Unapologetically chocolate. Marshmallow fudge frosting is everything. 

Plus, it’s one of those melt-your-own-frostings where everything is, yep you guessed it, melted on the stove until smooth and perfect. No electric mixers. No whipping butter. No clouds of powdered sugar clogging your sinuses. Nope, none of that. 

The marshmallow fudge frosting is just what the decadent brownies and crunchy peanut butter need to be a complete dessert. 

Let’s Talk Brownies

Although this recipe is made up of three layers, it’s super easy. (Not just saying that, promise.)

Start with a 9X13-inch pan of your favorite baked brownies. I’ve included my favorite one-bowl brownies in the recipe below, because they are AMAZING. But if you like your brownie recipe more than you like my brownie recipe, go ahead and use that. I promise, we can still be friends (I just won’t eat your brownies). Haha. Joking. Kind of. 🙂

The middle layer is one ingredient. Crunchy peanut butter. That’s it. If you’ve read my blog for any length of time, you know I’m one of the last people to encourage using nuts in brownies of any kind, but these rich brownies definitely benefit from the salty crunch of the tiny peanuts, and the creamy peanut butter acts a no-recipe frosting. Score. 

After the marshmallow fudge frosting is spread on top, these little brownies benefit from a quick chill session in the refrigerator. I’ve given tips for cutting even squares in the recipe notes below (spoiler alert: dip sharp knife in hot water, wipe clean, slice, repeat), and like I mentioned in the opening act up there, these peanut butter marshmallow fudge brownies are unreal chilled. Or frozen.  

I just can’t say enough good things about these brownies. They are a peanut butter and chocolate lover’s dream, and the salty, sweet, crunchy, fudgy, chewy combo is ridiculous (in a good way).

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Peanut Butter Marshmallow Fudge Brownies

Yield: 9X13-inch pan of brownies

Prep Time: 30 minutes

Cook Time: 30 minutes

Additional Time: 2 hours

Total Time: 3 hours

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Ingredients

Brownies (or use your favorite brownie recipe):

• 1/2 cup boiling water
• 2 ounces unsweetened chocolate, finely chopped
• 1/3 cup (1 ounce) unsweetened or Dutch-process cocoa powder
• 2 1/3 cups (17.5 ounces) granulated sugar
• 1/2 cup vegetable, canola, or other neutral-flavored oil (like avocado or grapeseed)
• 4 tablespoons butter, melted
• 2 large eggs + 2 large egg yolks
• 2 teaspoons vanilla extract
• 1 3/4 cups (8 3/4 ounces) all-purpose flour
• 1/2 teaspoon salt

Peanut Butter Layer:

• 1 1/2 cups (about 13.5 ounces) crunchy or creamy peanut butter

Marshmallow Fudge Layer:

• 10 large marshmallows or 1 1/4 cups mini marshmallows (about 2.75 to 3 ounces)
• 4 tablespoons (2 ounces, 1/4 cup) butter
• 1/4 cup milk (I use 2%)
• 1/4 cup (.75 ounce) unsweetened or Dutch-process cocoa powder (see note)
• 1/4 teaspoon salt
• 1 1/2 cups (6 ounces) powdered sugar

Instructions

1. For the brownies: Preheat oven to 350 degrees F. Line a 9X13-inch metal pan with aluminum foil and lightly grease with cooking spray (the lining of the pan is optional but helps with cleanup).
2. In a large bowl, whisk together the boiling water and chopped chocolate until smooth (if the chocolate doesn't melt fully, microwave the water/chocolate mixture for 20-30 seconds). Add the cocoa powder and whisk together. Add the sugar, oil, butter, eggs and vanilla. Mix until smooth and well-combined.
3. Add the flour and salt and mix until just combined and no white streaks remain. Spread the batter evenly in the prepared pan. Bake for 25-30 minutes until crackly on top and set around the sides. Let cool for 10-15 minutes.
4. While the brownies are still warm, dollop the peanut butter across the top. Let it sit for a few minutes so the peanut butter softens (alternately, you can warm the peanut butter in the microwave) and spread into an even layer. Refrigerate until the peanut butter is set, about an hour.
5. For the marshmallow frosting: in a microwave-safe bowl (or in a saucepan over low heat on the stove), combine the marshmallows, butter, milk, cocoa powder, and salt. Heat for 1-minute intervals, stirring in between, until melted and smooth.
6. Add the powdered sugar a little at a time to the warm chocolate mixture and stir until smooth and well-combined. If the frosting starts to get a little clumpy, heat for 20-second intervals in the microwave (or over low heat on the stove) until it smooths out a little.
7. Spread the fudge frosting over the chilled peanut butter layer. Refrigerate until set, about an hour. Serve the brownies chilled or at room temp (they are also tasty frozen). To easily cut the bars, run a sharp knife under very hot water, wipe clean, and slice (running under hot water between cuts).

Notes

You can substitute your favorite 9X13-inch brownie recipe for the base brownie layer if you'd like. 🙂 Using Dutch-process cocoa in the frosting will yield a darker/richer frosting.

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