01 -
Preheat the oven to 350°F (175°C). Line an 8-inch (20 cm) square baking pan with parchment paper, leaving an overhang on two sides.
02 -
In a large bowl, whisk together melted butter and granulated sugar until smooth.
03 -
Add eggs and vanilla extract; whisk until well combined.
04 -
Sift in flour, cocoa powder, salt, and baking powder. Fold gently until just combined—do not overmix.
05 -
Pour the brownie batter into the prepared pan and smooth the top.
06 -
In a small bowl, mix peanut butter, powdered sugar, and melted butter until smooth.
07 -
Drop spoonfuls of the peanut butter mixture evenly over the brownie batter. Use a knife or skewer to gently swirl the peanut butter into the chocolate batter, creating a marbled effect.
08 -
Bake for 28–32 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
09 -
Cool completely in the pan on a wire rack before lifting out and slicing into squares.