- 1 cup (2 sticks) unsalted butter, plus more for dish
- 2/3 cup all-purpose flour, plus more for dish
- 1/2 teaspoon salt
- 12 ounces good-quality semisweet chocolate, coarsely chopped
- 1 1/4 cups packed light-brown sugar
- 4 large eggs
- 1 tablespoon pure vanilla extract
- Preheat oven to 375 degrees. Butter a 9-by-13-inch baking dish. Dust with flour, and tap out excess; set aside. Whisk together flour and salt in a small bowl; set aside.
- Melt chocolate and butter in a heatproof bowl set over a pan of simmering water, stirring. Let cool completely.
- Meanwhile, put sugar and eggs into the bowl of an electric mixer fitted with the whisk attachment. Beat on high speed until pale, about 3 minutes. Reduce speed to low. Beat in chocolate mixture and the vanilla. Add flour mixture, and beat until just combined.
- Spread batter evenly into prepared dish. Bake until top has cracked, center is just firm to the touch, and a cake tester inserted into center comes out with moist crumbs, 25 to 30 minutes. Let cool completely in dish on a wire rack. Cut into squares.
Brownies can be stored in an airtight container up to 2 days.
Martha used an 8-by-8-inch baking pan, lined with parchment paper (2 sheets, each cut into a 16-by-8-inch rectangle), brushed with butter and dusted with cocoa powder.