Peanut Butter Swirl Brownies

• 8 tablespoons (1 stick) unsalted butter, cut into small pieces, plus more for pan
• 2 ounces good-quality unsweetened chocolate, coarsely chopped
• 4 ounces good-quality semisweet chocolate, coarsely chopped
• 2/3 cup all-purpose flour
• 1/2 teaspoon baking powder
• 1/4 teaspoon salt
• 3/4 cup granulated sugar
• 3 large eggs

• 4 tablespoons unsalted butter, melted
• 1/2 cup confectioners’ sugar
• 3/4 cup smooth peanut butter
• 1/4 teaspoon salt
• 1/2 teaspoon pure vanilla extract
• 2 teaspoons pure vanilla extract

Directions

1. Preheat oven to 325 degrees. Line a buttered 8-inch square baking pan with foil or parchment paper, allowing 2 inches to hang over sides. Butter lining (excluding overhang); set pan aside.
2. Make batter: Put butter and chocolates in a heatproof medium bowl set over a pan of simmering water; stir until melted. Let cool slightly.
3. Whisk together flour, baking powder, and salt in a separate bowl, and set aside.
4. Whisk granulated sugar into chocolate mixture. Add eggs, and whisk until mixture is smooth. Stir in vanilla. Add flour mixture; stir until well incorporated.
5. Make filling: Stir together butter, confectioners’ sugar, peanut butter, salt, and vanilla in a bowl until smooth.
6. Pour one-third of batter into prepared pan, and spread evenly with a rubber spatula. Place dollops of filling (about 1 tablespoon each) about 1 inch apart on top of batter. Drizzle remaining batter on top, and gently spread to fill pan. Place dollops of remaining filling on top.
7. With a butter knife, gently swirl filling into batter, running knife lengthwise and crosswise through layers. Bake until a cake tester inserted into brownies (avoid center and edges) comes out with a few crumbs but is not wet, about 45 minutes. Let cool slightly in pan, about 15minutes. Lift out brownies; let cool completely on a wire rack before cutting into squares.