* 8 tablespoons (1 stick) unsalted butter, cut into pieces, plus more for pan
* 1 cup all-purpose flour (spooned and leveled)
* 1/4 cup unsweetened cocoa powder
* 1/2 teaspoon baking powder
* 1/2 teaspoon salt
* 8 ounces semisweet or bittersweet chocolate, chopped
* 1 1/4 cups sugar
* 3 large eggs
1. Preheat oven to 350 degrees. Brush a 9-inch square baking pan with butter. Line bottom and two sides with a strip of parchment paper, leaving a 2-inch overhang on the two sides. Butter paper, and set pan aside. In a small bowl, whisk flour, cocoa, baking powder, and salt; set aside.
2. Place butter and chocolate in a large heatproof bowl set over (not in) a saucepan of gently simmering water. Heat, stirring occasionally, until smooth, 2 to 3 minutes, remove bows from pan. Add sugar, mix to combine. Add eggs, and mix to combine. Add flour mixture, mix just until moistened (do not overmix). Transfer, batter to prepared pan, smooth top.
3. Bake until a toothpick inserted in center comes out with a few moist crumbs attached, 50 to 60 minutes. Cool in pan for 30 minutes. Using paper overhang, lift brownies out of pan; transfer to a rack to cool completely (still on paper). On a cutting board, using a dampened serrated knife, cut into 16 squares. Store in an airtight container at room temperature, up to 2 days.