Always remember: The better the chocolate, the better the brownie.
- 1 cup coarsely chopped walnuts (optional)
- 1 cup (2 sticks) unsalted butter, plus more for pan
- 8 ounces best-quality unsweetened chocolate, such as Callebaut or Valrhona
- 5 large eggs
- 3 1/2 cups sugar
- 2 teaspoons instant espresso
- 1 tablespoon pure vanilla extract
- 1 2/3 cups sifted all-purpose flour
- 1/2 teaspoon salt
- 1/2 cup semisweet chocolate chips
Heat oven to 350 degrees. Spread chopped walnuts on a baking pan; toast until fragrant, 5 to 10 minutes. Transfer nuts to a bowl to cool.
Raise oven temperature to 400 degrees. Generously butter a 9-by-13-inch baking pan; set aside.
Combine chocolate and butter in a heat-proof bowl or the top of a double boiler. Set over a pan of simmering water until the chocolate mixture has melted. Remove from heat; set aside.
In the bowl of an electric mixer fitted with the paddle attachment, beat eggs, sugar, and espresso at high speed, 10 minutes. Reduce speed to low, and add melted-chocolate mixture and the vanilla; beat until combined. Slowly add flour and salt; beat just until incorporated. Fold in chocolate chips and toasted walnuts. Pour the batter into the prepared pan.
Bake until edges are dry but center is still soft, about 35 minutes. Remove pan from oven, and transfer to a wire rack to cool. Cut into 3-inch squares.