Chocolate Angel Food Cake Recipe

1 Preheat oven to 325 degrees F.
2 In a medium bowl, mix confectioners' sugar, cake flour, and cocoa. Sift together 5 times, and set aside.
3 In a clean large bowl, whip egg whites, salt, and cream of tartar with an electric mixer on high speed until very stiff. Fold in white sugar 2 tablespoons at a time. Fold in flour mixture, a little at a time, until fully incorporated. Stir in vanilla. Pour into a 10 inch tube pan.
4 Bake at 325 degrees F for approximately 1 hour .