10 tablespoons unsalted butter, cut into 1-inch pieces
1¼ cups sugar
¾ cup natural unsweetened cocoa powder (spooned into cup to measure, then leveled)
1 teaspoon vanilla extract
¼ teaspoon salt
2 large eggs, chilled
⅓ cup plus 1 tablespoon unbleached all-purpose flour
1 cup walnut pieces
Position rack in bottom third of oven; preheat to 325ºF. Line 8-inch square metal pan with foil, as shown here. Butter the foil.
Melt butter in medium saucepan over medium heat. Continue cooking until butter stops foaming and browned bits form at bottom of pan, stirring often, about 5 minutes. Remove from heat; immediately add sugar, cocoa, 2 teaspoons water, vanilla, and salt. Stir to blend. Let cool 5 minutes (mixture will still be hot.) Add eggs to hot mixture 1 at a time, beating vigorously to blend after each addition. When mixture looks thick and shiny, add flour and stir until blended. Beat vigorously 60 strokes. Stir in nuts. Transfer to prepared pan.
Bake brownies until toothpick inserted into center comes out almost clean (with a few moist crumbs attached), about 25 minutes. Cool in pan on rack. Using the foil overhang, lift brownies from pan. Cut into squares and serve. (Alternatively, wrap tightly with plastic and refrigerate for up to 3 days. Cut when ready to serve.)