Peanut Butter Cup Brownies

For the peanut butter swirl:
Pour melted butter into a medium bowl. Sift in powdered sugar. Add salt. Stir until combined. Add peanut butter and flour and stir until smooth. Set aside.

For the brownies:
Preheat oven to 325ºF. Line a 9×13 inch pan with foil and grease.

Melt butter in a saucepan over low heat. Stir in sugars and heat while stirring until hot to the touch, but not bubbling. Remove pan from heat and whisk in cocoa powder, vanilla, salt, and baking powder. Whisk in eggs, one at a time, until incorporated. Stir in flour.

Spread 1/2 of the batter evenly in the prepared pan. Place peanut butter cups in six rows of 4. Pour remaining batter as evenly as possible across the top. Dollop the peanut butter swirl on top. Lightly swirl into the brownie batter with an offset spatula, taking care not to disturb the peanut butter cups. Bake for 30–35 minutes. The brownies will be set and the peanut butter swirl may be slightly tacky. It will set up as it cools.

Remove brownies from the oven, place on a wire rack, and let cool completely in the pan. Cut the brownies using a bench scraper.