Brownie layer: 6 oz (170g) 70% dark chocolate chips, chopped
12 tbsp (165g) salted butter (1½ sticks)
1⅓ cups (265g) granulated sugar
1½ tsp vanilla
3 large eggs, room temperature
1 cup (125g) all-purpose flour
1 tbsp (6g) cocoa powder
1 tsp baking powder
Recipe
Preheat oven to 350°F. Butter or spray a 9-inch square pan, or line with parchment.
Make peanut butter layer: mix peanut butter, melted butter, vanilla, and confectioners sugar together. Set aside.
Make brownie layer: melt chocolate and butter together (microwave or stovetop). Whisk in sugar, then vanilla, then eggs one at a time. Sift together flour, cocoa, and baking powder; mix into chocolate mixture until just combined.
Pour ¾ of the brownie batter into the pan and spread to the corners. Drop spoonfuls of peanut butter mixture onto the batter. Spoon remaining brownie batter among the peanut butter dollops. Swirl together with a knife. Add extra chocolate chunks on top if desired.
Bake about 40 minutes until a tester comes out with only a few moist crumbs. Cool before slicing.