In an extra-large mixing bowl allow egg whites to stand at room temperature for 30 minutes. Meanwhile, sift the 1-1/2 cups powdered sugar, flour, and cocoa powder together 3 times; set aside.
Add cream of tartar and the 1 teaspoon vanilla to egg whites. Beat with an electric mixer on medium to high speed until soft peaks form (tips curl). Gradually add granulated sugar, about 2 tablespoons at a time, beating on medium to high speed until stiff peaks form (tips stand straight).
Sift about one-fourth of flour mixture over the beaten egg whites; fold in gently. Repeat, folding in remaining flour mixture by fourths. Pour into an ungreased 10-inch tube pan. Gently cut through the cake batter with a narrow metal spatula or knife.
Bake on the lowest rack in a 350 degree F oven for 40 to 45 minutes or until top springs back when lightly touched. Immediately invert cake (leave in the pan); cool thoroughly. Using a narrow metal spatula, loosen the sides of the cake from the pan. Remove cake from the pan.
For glaze, combine the 1 cup powdered sugar, the 1/4 teaspoon vanilla, and enough of the coffee liqueur (about 2 tablespoons), 1 teaspoon at a time, to make of drizzling consistency. Drizzle over top of the cake. Makes 12 servings.