Flourless cooking spray for greasing
3/4 cup (11/2 sticks) unsalted butter
4 oz. unsweetened chocolate, chopped
2 large eggs
11/3 cups sugar
2 teaspoons vanilla extract
1/4 teaspoon salt
1/4 cup cake flour, sifted
3/4 cup coarsely chopped toasted walnuts
Preheat the oven to 350°F. Lightly spray a 9-inch square baking pan with cooking spray or line it with parchment paper, leaving an overhang on 2 sides to help remove the brownies from the pan.
Melt the butter and chocolate in a saucepan over low heat or in a bowl in the microwave in 15- to 20-second intervals, stirring and blending gently with a spoon.
In a stand mixer fitted with the whisk attachment, whip the eggs, sugar, vanilla extract and salt together on high speed, scraping down the bowl with a rubber spatula as needed, until thick and light in color, 4–5 minutes.
While stirring, pour some of the egg mixture into the melted chocolate mixture to lighten it, then pour the chocolate mixture into the remaining egg mixture and blend on medium speed, scraping down the bowl as needed. Mix in the flour and nuts on low speed until just blended. The batter will be very wet. Pour the batter into the prepared pan and spread evenly.
Bake until a skewer inserted into the center of the brownies comes out with a few moist crumbs still clinging to it, rotating the pan as necessary to bake evenly, 30–40 minutes. Allow the brownies to cool completely in the pan on a wire rack. Use the parchment overhang to help unmold the brownie bar, then cut into 3-inch-square pieces.
Makes 9 brownies.
Note: To make brownie ice cream sandwiches:
Prepare the recipe using a 9-by-13 baking pan, as opposed to a square 9-by-9 baking pan, and reduce baking time to 25-30 minutes, to yield a thinner brownie. Place a scoop of your favorite ice cream flavor on one half of the square, and allow the scoop to soften for a few minutes. Using a non-stick spatula, flatten the scoop, and then top with another brownie to complete your sandwich.