1/2 cup unsweetened cocoa
1-2/3 cups egg whites (12 to 14 large egg whites)
1-1/2 teaspoons cream of tartar
3/4 teaspoon salt
1-1/2 teaspoons vanilla extract
2 cups sugar
Preheat over to 375 degrees. Place flour and cocoa in coarse sieve; with spoon, press flour mixture into small bowl; set aside.
In large bowl, with mixer at high speed, beat egg whites cream of tartar, and salt until soft peaks form; add vanilla extract. Beating at high speed, sprinkle in sugar, 2 tablespoons at a time, eating until sugar completely dissolves and whites stand in stiff peaks. With rubber spatula or wire whisk, fold in flour mixture just until flour mixture disappears.
Pour batter into un-greased 10-inch tube pan. Bake 30 to 35 minutes, until cake springs back when lightly touched with finger. Invert cake in pan on funnel or bottle, cool completely in pan.
To serve with metal spatula, carefully loosen cake from pan; place on cake plate bottom-side up.
To make chocolate glaze if desired:
4-1 ounce squares semisweet chocolate
2 teaspoons shortening
In heavy small saucepan over low heat, heat semisweet chocolate and shortening until melted and smooth, stirring frequently. Spread melted chocolate over top of cake, letting some run down side.