- 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.