Fudge Brownies

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...