Dollops of peanut butter filling are spooned onto brownie batter; pulling a knife back and forth through both results in a marbleized look.

　　

Ingredients

makes 9 large or 16 small

　　

for the batter

1/2 cup (1 stick) unsalted butter, cut into small pieces, plus more for pan

　　2 ounces unsweetened chocolate, coarsely chopped

　　4 ounces semisweet chocolate, coarsely chopped

　　2/3 cup all-purpose flour

　　1/2 teaspoon baking powder

　　1/4 teaspoon coarse salt

　　3/4 cup granulated sugar

　　3 large eggs

　　2 teaspoons pure vanilla extract

　　

for the filling

4 tablespoons (1/2 stick) unsalted butter, melted

　　1/2 cup confectioners’ sugar

　　3/4 cup smooth peanut butter

　　1/4 teaspoon coarse salt

　　1/2 teaspoon pure vanilla extract

　　

Step 1

Preheat oven to 325°F. Butter an 8-inch square baking pan and line with parchment, allowing a 2-inch overhang. Butter lining (not overhang).

　　

Step 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.

　　

Step 3

Whisk granulated sugar into chocolate mixture. Add eggs, and whisk until mixture is smooth. Stir in vanilla. Add flour mixture; stir until well combined.

　　

Step 4

Make filling: Stir together butter, confectioners’ sugar, peanut butter, salt, and vanilla in a bowl until smooth.

　　

Step 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 peanut butter mixture on top. Gently swirl peanut butter filling into batter with a butter knife, running the knife lengthwise and crosswise through layers.

　　

Step 6

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 15 minutes. Lift out; let cool completely on a wire rack before cutting into squares. Brownies can be stored in an airtight container at room temperature up to 3 days.

　　

HOW TO MARBLEIZE BROWNIES

Step 7

Use two large spoons to drop dollops of filling over a base of chocolate batter. Add more batter on top, then more dollops of filling. Drag a butter knife back and forth with the tip touching the bottom of the pan.

　　Martha Stewart's Cookies