Peanut Butter Brownies Recipe

These peanut butter brownies are fudgy cocoa brownies baked in an 8×8 inch pan with a marbled peanut butter swirl on top. One bowl, no mixer, 25 to 30 minutes at 350°F, and you get 16 squares about 2 inches across.

Most of the work is knowing when to stop: stop stirring once the flour disappears, stop swirling while the lines still look sharp, and take the pan out while a toothpick still shows moist crumbs.

What Keeps a Cocoa Brownie Fudgy

No melted chocolate here. The fudginess comes from the balance: 115 g butter and 200 g sugar against only 65 g flour, with 40 g cocoa for the chocolate flavour. That much fat and sugar with so little flour gives a dense, chewy square instead of a cake.

Whisk the melted butter and sugar until glossy, then whisk in the eggs and vanilla until the mix looks slightly thicker. That step dissolves some of the sugar, which is what gives the top its thin shine. After the dry ingredients go in, switch to a spatula and stir only until no streaks remain. Extra mixing builds gluten and turns the squares cakey.

If you like this kind of all-cocoa base, my cocoa powder brownies work the same way without the swirl.

Natural or No Stir Peanut Butter for the Swirl?

Creamy, either way. Crunchy bits catch on the knife and break up the marbling. The swirl is 1/3 cup (85 g) peanut butter stirred with 2 tablespoons powdered sugar, which sweetens it slightly and thickens it so it holds a line.

• No stir creamy (the shelf-stable kind): holds the sharpest swirl lines and bakes up soft and fudge-like on top. The easier choice for a first pan.
• Natural peanut butter: tastes more of roasted peanuts and less sweet. Stir the oil back in very well first, or the swirl leaves greasy streaks. Pick a creamy jar that is not too runny.

Homemade works too if it is smooth; here is how to make peanut butter at home.

Mixing the One Bowl Batter

Heat the oven to 350°F (175°C) and line the 8×8 inch pan with parchment, leaving some overhang on two sides so you can lift the slab out later. Whisk the butter, sugar, eggs and vanilla as above.

Sift the cocoa, flour, salt and baking powder over the top. Do sift. Cocoa clumps, and small dry lumps stay as bitter pockets in a batter you are trying not to overmix.

The batter should be thick and glossy, closer to frosting than to cake batter. Spread it right into the corners, pushing it up against the parchment with the back of the spatula so the edges bake as thick as the middle.

Marbling the Top So the Swirl Stays Visible

Stir the peanut butter and powdered sugar together. If it is stiff, warm it in the microwave for 10 to 15 seconds so it drops off the spoon in soft dollops. Cold peanut butter drags the batter along with it and muddies the pattern.

Drop small spoonfuls evenly over the batter, about 9 to 12 dots. Then run a butter knife or skewer through them just under the surface, in 6 to 8 passes across and back. Stay shallow. Go deep and the peanut butter sinks into the middle of the pan, out of sight, and the top bakes plain brown with only a faint outline where the swirl used to be.

Want a Thicker Peanut Butter Layer on Top?

Double the swirl mixture, drop it on and spread it gently into an even layer instead of marbling. Start checking at 25 minutes as usual. For something more like a candy bar, the chocolate peanut butter brownies are a layered version with candy pieces, and the buckeye brownies add a peanut butter filling under a chocolate top.

Baking Until Moist Crumbs, Not Clean

Bake 25 to 30 minutes. They are done when the edges look set and pull slightly from the paper, and a toothpick pushed in near the centre comes out with a few moist crumbs but no wet batter. Test in plain brownie. A peanut butter streak always looks wet.

Clean? Too far. The centre keeps firming as the pan cools on a rack, so take them out a minute early rather than late. A glass pan holds heat longer than metal, so check at the earliest time.

Cutting 16 Squares and Keeping Them Chewy

Cool the brownies completely in the pan, then lift them out by the parchment. For clean edges, chill the slab for 30 minutes and cut with a sharp knife warmed under hot water, wiping it dry between cuts. Three cuts each way give you 16.

Store them in an airtight container at room temperature for up to 3 days, or in the fridge for up to a week. Cold brownies are firmer and very fudgy; give them 15 minutes on the counter if you want them softer. They pack well for lunchboxes because the swirl is baked in and does not smear.

Melted Butter or Brown Butter in the Batter

I have made these with both. Melted butter keeps the cocoa up front. Brown butter is my pick for a make-ahead pan. It adds a toasty, nutty note that goes well with the peanut butter and shows more on the second day. Cook it until the solids turn golden and it smells like toffee, then let it cool a few minutes before whisking in the sugar so it does not scramble the eggs.

Short Answers for Swirled PB Brownies

Can I add this peanut butter swirl to a boxed brownie mix?

Yes. Make an 8×8 inch pan of boxed batter, then add the same 1/3 cup peanut butter and 2 tablespoons powdered sugar swirl and bake as the box says.

Can I skip the powdered sugar?

Yes, it is optional. The swirl will taste saltier and less sweet and spread a little more in the oven.

Do they need frosting?

No, but for a party pan a thin layer of peanut butter frosting or a chocolate brownie frosting works once they are completely cool.

Can I double the recipe?

Yes, in a 9×13 inch pan. The batter sits a little deeper than in an 8×8 pan, so it may need a few extra minutes; trust the moist crumb toothpick test over the clock.

For more ideas with the same two flavours, browse the peanut butter recipes, or try the no-bake peanut butter bars when the oven is busy.