- 2 sticks (1 cup) unsalted butter
- 8 ounces bittersweet (60 percent cacao) chocolate, coarsely chopped, such as Ghirardelli or Callebaut
- 1 1/4 cups (6 1/2 ounces) all-purpose flour
- 1 teaspoon baking powder
- 1 1/2 tablespoons cocoa powder
- 3/4 teaspoon kosher salt
- 2 cups (14 ounces) granulated sugar
- 4 large eggs, at room temperature
- 2 teaspoons vanilla extract
- 1 large bag (about 26 pieces) York Peppermint Patties
- Put oven rack in middle position, and preheat oven to 350°F. Grease a 9-by-13-inch baking pan with butter; line pan with parchment paper, leaving a 2-inch overhang on 2 sides.
- Melt butter and chocolate in a medium heatproof mixing bowl set over a saucepan of simmering water, stirring occasionally, until smooth.
- Whisk together flour, baking powder, cocoa powder, and salt in a small mixing bowl.
- Whisk together sugar, eggs, and vanilla in a large bowl, then pour in chocolate mixture, whisking until combined well. Fold in the flour mixture until just combined.
- Spread about half of the batter in the prepped pan. Arrange the Peppermint Patties evenly on top, and then spread the remaining batter on top of the Peppermint Patties.
- Bake until the top is shiny, the sides have begun to pull away slightly from the pan, and the center has puffed up (a wooden pick or skewer will not come out entirely clean), about 40-45 minutes.
- Cool brownies completely in the pan on a wire rack. Very carefully transfer the brownies from the pan to a cutting board using the parchment sling. Cut out the brownies using a large heart cookie cutter.