Line a 9x5x3-inch loaf pan with foil, extending foil over ends. Grease foil; set pan aside. In a small saucepan stir together sugar, butter, and cocoa powder. Cook and stir over medium heat until butter is melted. Remove from heat; cool for 5 minutes.
Add the egg and vanilla to cocoa mixture. Using a wooden spoon, beat lightly just until combined. Stir in the flour, baking powder, and salt. Stir in walnuts. Spread the batter in the prepared loaf pan.
Bake, uncovered, in a 350 degrees oven for 12 to 15 minutes or until a toothpick inserted near center comes out clean. Cool in pan on a wire rack. Using the ends of foil, lift brownies out of pan. If desired, frost with Cocoa Glaze. Cut into triangles. Makes 6 brownies.
In a small bowl combine sifted powdered sugar, cocoa powder, softened butter, and vanilla. Beat in enough hot water (2 to 4 teaspoons) to make a glaze of spreading consistency.