Cocoa Angel Food

Beat the whites of five eggs until very foamy, add one-fourth teaspoonful cream of tartar and beat until dry. Then gradually add one cupful of sifted sugar which has been mixed with one-fourth cupful of cocoa. Add vanilla, one-half cupful of flour and one-half tablespoonful of cornstarch, which has been sifted many times. Bake in a tube pan one-half hour.