Prep time: 10 minutes
Cook Time: 1 hour
Total time: 1 hour and 10 minutes + cooling
Yield: 16 brownies
1/2 cup (1 stick) melted butter
4 large eggs
1 ½ cups light brown sugar, firmly packed
1 teaspoon pure vanilla extract
1 cup all-purpose flour
1 teaspoon baking powder
1 (12-ounce) bag semisweet chocolate chips, melted
1 cup Smooth Operator peanut butter
1. Preheat oven to 350°F. Butter an 8-inch square baking pan and line with parchment (with an overhang on two sides). In a large bowl, stir together butter, eggs, sugar, and vanilla until combined; stir in flour and baking powder. Transfer 1/2 cup batter to a bowl with peanut butter, mixing to incorporate; stir melted chocolate into remaining batter.
2. Pour brownie batter into prepared pan; dollop with peanut butter mixture. Use a knife to swirl dollops into batter. Bake until brownies are puffed and a knife (when inserted in the center of the brownie cake) tests clean, about 50 to 60 minutes. Cool brownies in pan set on a wire rack. Cut into 16 brownies.