- 1/2 cup (1 stick) unsalted butter, plus more for the pan
- 3/4 cup all-purpose flour, spooned and leveled
- 1/4 cup unsweetened cocoa powder
- 1/2 teaspoon baking powder
- 1/2 teaspoon kosher salt
- 6 ounces semisweet chocolate, chopped
- 1 cup sugar
- 2 large eggs
- 1 teaspoon pure vanilla extract
- 1 1/2 cups chopped mini peanut butter cups (about 20)
- Heat oven to 350° F. Butter an 8-inch square baking pan. Line with 2 crisscrossed pieces of parchment, buttering in between and leaving an overhang on all sides; butter the top piece of parchment.
- In a medium bowl, whisk together the flour, cocoa, baking powder, and salt; set aside.
- In a large microwave-safe bowl, combine the butter and chocolate. Microwave on high in 30-second intervals, stirring between each, until melted and smooth. Let cool slightly. Whisk in the sugar, eggs, and vanilla until smooth.
- Add the flour mixture and mix until just combined (do not overmix). Fold in the peanut butter cups.
- Spread the batter in the prepared pan and bake until a toothpick inserted in the center comes out clean, 30 to 35 minutes. Let cool completely in the pan.
- Holding the paper overhang, lift the brownies out of the pan and transfer to a cutting board. Cut into 16 squares (4 rows by 4 rows).