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Peanut Butter Swirl Brownies

adapted from Martha Stewart

Ingredients

For the batter:

  • 8 tablespoons 1 stick unsalted butter, cut into small pieces, plus more for pan
  • 6 ounces good-quality semisweet chocolate coarsely chopped
  • ⅔ cup all-purpose flour
  • ½ teaspoon baking powder
  • ¼ teaspoon salt
  • ¾ cup granulated sugar
  • 3 large eggs
  • 2 teaspoons pure vanilla extract

For the filling:

  • 4 tablespoons unsalted butter melted
  • ½ cup confectioners’ sugar
  • ¾ cup smooth peanut butter
  • ¼ teaspoon salt
  • ½ teaspoon pure vanilla extract

Instructions

  1. Preheat oven to 325 degrees. Butter an 8-inch square baking pan and line with parchment, allowing a 2-inch overhang. Butter lining (not overhang).
  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. Whisk together flour, baking powder, and salt in a bowl.
  3. Whisk granulated sugar into chocolate mixture. Add eggs, and whisk until mixture is smooth. Stir in vanilla. Add flour mixture; stir until well incorporated.
  4. Make filling: Stir together butter, confectioners’ sugar, peanut butter, salt, and vanilla in a bowl until smooth.
  5. Pour one-third of batter into prepared pan; spread evenly with a rubber spatula. Drop dollops of peanut butter filling (about 1 tablespoon each) on top of batter, spacing about 1 inch apart. Drizzle remaining batter on top, and gently spread to fill pan. Drop dollops of remaining filling on top. Gently swirl peanut butter filling into batter with a butter knife, running the knife lengthwise and crosswise through layers.
  6. Bake until a toothpick inserted into brownies comes out with a few crumbs but is not wet, about 45 minutes. Let cool slightly in pan, about 15 minutes. Lift out; let cool completely on a wire rack before cutting into squares