Ingredients
1/2 cup (1 stick) unsalted butter, plus more for pan
1 cup all-purpose flour, (spooned and leveled)
1/4 teaspoon baking powder
1/8 teaspoon salt
2 ounces unsweetened chocolate, coarsely chopped
1 ounce semisweet chocolate, coarsely chopped
1 cup packed dark-brown sugar
1/4 cup granulated sugar
2 large eggs
1 teaspoon pure vanilla extract
1 cup pecans, coarsely chopped
Preparation
Preheat oven to 350 degrees. Butter an 8-inch-square baking pan. Line bottom with parchment paper, leaving an overhang on two sides. Butter paper; set pan aside. In a medium bowl, whisk together flour, baking powder, and salt; set aside.
Place butter and chocolates in a large heatproof bowl set over (not in) a saucepan of simmering water. Heat until smooth, 2 to 3 minutes, stirring occasionally. Remove from heat, and stir in sugars, eggs, vanilla, flour mixture, and half of pecans. Transfer batter to prepared pan; smooth top. Sprinkle with remaining pecans.
Bake until a toothpick inserted in center comes out clean, 30 to 35 minutes. Set pan on a wire rack; let cool completely. Using paper overhang, lift brownie onto a cutting board; cut into 16 squares.