Chocolate Peanut Butter Swirl Brownies

These chocolate peanut butter swirl brownies start with a box mix but taste completely homemade. Fudgy, rich, and topped with a creamy peanut butter swirl, they are the easiest way to upgrade classic brownies.

Chocolate Peanut Butter Box Brownies

As a working mom with busy teens always coming and going, shortcut recipes are my saving grace. I love taking something simple, like a box of brownie mix, and turning it into something that feels homemade and special like these and my chocolate peanut butter crunch brownies.

After sharing my cherry brownies and Oreo stuffed brownie cups, I knew everyone would love these chocolate peanut butter swirl brownies. They’re rich, fudgy, and swirled with creamy peanut butter, but still easy enough to make on a random weeknight when everyone suddenly wants dessert.

Ingredient Notes

Find the full recipe with printable directions below.

• Fudge brownie mix: I used an 18.3 ounce fudge brownie mix for thick, rich chocolate flavor. If you use a 16.3 ounce box, reduce the water to 2 tablespoons so the batter stays nice and fudgy.
• Eggs, oil, and water: These are the standard box mix add-ins. Vegetable oil gives the brownies a soft, moist texture, but you can substitute canola oil.
• Semi-sweet chocolate chips: Folding in chocolate chips makes these extra gooey and chocolatey. You can swap in dark chocolate chips for a deeper flavor or milk chocolate for a sweeter bite.
• Creamy peanut butter: Use regular creamy peanut butter for the smoothest swirl. Natural peanut butter can separate and may not marble as nicely.
• Powdered sugar: A little powdered sugar sweetens and smooths the peanut butter so it spreads and swirls easily over the brownie batter.

How to Make Chocolate Peanut Butter Swirl Brownies

In a large bowl, stir together the brownie mix, eggs, oil, and water until combined. Fold in the chocolate chips, then spread the thick batter evenly into the prepared pan.

In a microwave safe bowl, heat the peanut butter for about 30 seconds until smooth. Stir in the powdered sugar until creamy and fully combined.

Drop spoonfuls of the peanut butter mixture over the brownie batter.

Use the tip of a knife to gently swirl it into the top. Do not overmix. A few simple swirls will give you that pretty marbled look.

Bake for 28 to 30 minutes, or until a toothpick inserted in the center comes out mostly clean with a few moist crumbs. Let them cool before slicing so you get clean, fudgy squares.

Recipe Tips

• Do not overbake. Brownies continue to set as they cool. Pull them out when a toothpick has a few moist crumbs, not wet batter. Overbaking will make them dry instead of fudgy.
• Do not over swirl. Less is more when swirling the peanut butter. A few gentle figure eights with a knife will give you that pretty marbled look without blending it completely into the batter.
• Line the pan for easy removal. If you want super clean slices, line your pan with parchment paper and leave a little overhang. Once cooled, lift the whole slab out and slice on a cutting board.
• Let them cool completely. know it is tempting, especially with teens hovering in the kitchen. But letting the brownies cool helps them set and gives you cleaner, fudgier squares.