Ingredients

2 tablespoons granulated sugar 

2/3 cup sweetened condensed milk 

1 1/4 cups unsweetened shredded coconut 

1 large egg 

1/2 teaspoon pure vanilla extract 

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 

2 teaspoons pure vanilla extract 

Preparation

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.

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 separate bowl, and set aside.

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

Make filling: Stir together sugar, condensed milk, coconut, egg, and vanilla in a medium bowl; set aside.

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.

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 15 minutes. Lift out brownies; let cool completely on a wire rack before cutting into squares.