Re-sift cake flour with cocoa powder, 3/4 cup sugar and salt. Beat egg whites on low speed 1-1/2 minutes until frothy. Sprinkle in cream of tartar. Continue beating on medium speed, slowly adding remaining sugar. Beat egg whites 2 minutes or until soft (not stiff) peaks form. Beat in vanilla. Sprinkle 1/3 of cocoa mixture over egg whites. Fold in with rubber spatula, keeping spatula in batter under surface. Repeat twice with remaining cocoa mixture. Do not over-fold. Pour into 10-inch tube pan and bake in lower third of 325-degree oven about 35 minutes, or until cake springs back when touched. Remove pan from oven. Invert pan onto counter and let cool about 2 hours before removing cake. Makes 16 servings. Each serving contains about: 111 calories; 128 mg sodium; 0 cholesterol; 1 gram fat; 26 grams carbohydrates; 3 grams protein; 0.23 gram fiber. dess 108