Fudgy boxed brownies get a pillow-soft marshmallow layer and a crisp peanut butter–chocolate Rice Krispie topping for a contrast of gooey and crunchy in every bite.
Hands-off to assemble and party-ready after chilling, these bars take about 10 minutes to prep plus the bake time called for on your brownie mix and at least 2 hours to chill so the topping sets before slicing.
Why You’ll Love These Brownies
Do not cut the brownies before the topping has set — refrigerate the finished pan for at least 2 hours, or the bars will be sticky and fall apart. These make Servings: 16 servings, require about 10 minutes prep plus the bake time on your box, and are ideal for make-ahead parties. For another peanut-butter-forward treat, try Peanut Butter Brownie Batter Dip.
Line a 9×13 pan with parchment for easy lifting and cleaner cuts after chilling — that small step makes slicing and serving much easier.
Ingredients You’ll Need
How to Make the Brownies
- Preheat the oven to the temperature directed on your brownie package.
- Line a 9×13 pan with parchment paper so you can lift the finished brownies from the pan for easy slicing.
- Prepare the brownies according to the package directions and bake in the lined 9×13 pan.
- About 4 minutes before the brownies are fully baked, remove the pan from the oven and evenly scatter the 4 cups miniature marshmallows over the top.
- Return the pan to the oven and bake 4 more minutes to soften the marshmallows—this makes them easy to spread into an even layer.
- Remove the pan from the oven and, while still warm, gently spread the softened marshmallows into a single layer over the brownies. Allow the pan to cool completely at room temperature.
- In a microwave-safe bowl combine the 1-1/3 cups semi-sweet chocolate chips, 1 cup creamy peanut butter, and 3 tablespoons unsalted butter.
- Microwave the mixture on high for 30 seconds, then stir; continue heating in 15–30 second bursts, stirring in between, until the chocolate is melted and the mixture is smooth and glossy.
- Fold in the 2 cups crispy rice cereal until evenly coated; the cereal should remain crisp and form loose clusters.
- Drop spoonfuls of the chocolate–peanut butter–rice crisp mixture over the cooled marshmallow layer and spread as evenly as possible with a spatula.
- Refrigerate the brownies for at least 2 hours so the topping firms up—this chill time is essential to get clean, non-sticky bars.
- Use the parchment to lift the chilled slab from the pan and cut into squares with a sharp knife. If needed, warm the knife under hot water and dry it between cuts for cleaner slices.
Set the Topping Properly
The key to neat squares is patience: give the chocolate–peanut butter Rice Krispie topping time to cool and firm in the refrigerator. If you rush cutting, the topping will smear and the bars will fall apart.
- Chill for at least 2 hours; longer if the kitchen is warm.
- If the topping seems loose after chilling, press gently with a spatula to compact it and return to the fridge for another 30–60 minutes.
- Refrigerate uncovered so excess surface moisture won’t trap condensation between layers.
Choose the Right Mix
Not all boxed mixes are the same size. An 18 ounce mix gives the intended brownie depth in a 9×13 pan; 17–20 ounce mixes are workable but will alter thickness slightly.
- Line the pan with parchment so you can lift the brownies out cleanly after chilling.
- Follow the box directions for baking time, watching closely as you approach the end so you can add marshmallows 4 minutes before the end.
Lift and Cut Cleanly
Lifting the chilled slab out of the pan and using a heated, wiped knife will give the cleanest slices and prevent sticking.
- Use the parchment to pull the set brownies from the pan before slicing.
- For neat edges, dip a sharp knife in hot water, dry it, and slice; repeat between cuts for the best results.
Tips for Success
Chill completely: Do not cut before the topping is fully set — refrigerate at least 2 hours. If the topping still seems soft, extend chill time until it’s firm.
Microwave melting: Heat the chocolate, peanut butter, and butter in short bursts (30 seconds, then 15–30 as needed), stirring between each to avoid scorching and to judge when the mixture is smooth enough to fold in cereal.
Brownie mix size: Use an 18 ounce mix if possible; mixes from 17–20 ounces will still work but may change brownie thickness slightly.
Even topping: Press the rice crisp topping gently to compact it slightly if it’s too loose before chilling, and refrigerate uncovered so it sets firm.
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Storage & Make-Ahead
Store cooled and chilled brownies in an airtight container in the refrigerator; they hold well for several days and are easy to transport for parties once firm.
For longer storage, wrap individual squares and freeze; thaw in the refrigerator before serving so the topping stays intact.
Peanut Butter Rice Krispie Brownies
Equipment
- 9×13 Dish
Ingredients
- 1 18 ounce brownie mix
- 4 cups miniature marshmallows
- 1-1/3 cups semi-sweet chocolate chips
- 1 cup creamy peanut butter
- 3 tablespoons unsalted butter
- 2 cups crispy rice cereal
Instructions
- Preheat oven to the temperature directed on the brownie package.
- Line a 9×13 pan with parchment paper.
- Prepare the brownies according to the box directions.
- About 4 minutes before the brownies are fully cooked, remove the pan from the oven and evenly top the brownies with the miniature marshmallows.
- Return the pan to the oven and bake 4 more minutes to soften the marshmallows.
- Remove from the oven and spread the softened marshmallows into an even layer; let the brownies cool completely.
- In a microwave-safe bowl, combine the semi-sweet chocolate chips, creamy peanut butter, and unsalted butter.
- Microwave on high for 30 seconds, stir, and repeat heating and stirring until the chocolate is melted and the mixture is smooth.
- Add the crispy rice cereal and stir to combine.
- Drop spoonfuls of the chocolate and peanut butter rice crisp mixture over the marshmallow layer and spread as evenly as possible.
- Refrigerate the brownies for at least 2 hours to chill and let the topping set.
- Lift the brownies from the pan using the parchment paper and cut into squares.
