6 ounces espresso-flavored sweet dark chocolate, coarsely chopped
1 1/2 sticks (6 ounces) unsalted butter
2 tablespoons unsweetened cocoa powder
2 large eggs
1 cup sugar
2 teaspoons pure vanilla extract
1 cup all-purpose flour
Scant 1/4 teaspoon salt
Preheat the oven to 350°. Lightly butter a 9-inch square baking pan. Melt the chocolate and butter in a heatproof bowl set over a saucepan with 1 inch of simmering water. Remove from the heat, stir in the cocoa powder and let cool.
In a large bowl, beat the eggs at medium speed for 1 minute. Add the sugar and beat until the mixture is pale yellow, about 2 minutes. Fold in the melted chocolate and vanilla. Sift the flour over the batter, add the salt and fold in just until combined. Spread the batter evenly in the prepared pan.
Bake the brownies for about 45 minutes, or until a toothpick inserted in the center comes out clean. Let cool before cutting into squares.