Make a custard by beating together beaten egg yolks, sugar, lemon juice and peel. Cook custard over hot (not boiling) water, until mixture coats a spoon. Remove from heat. Soften gelatin in water and add to custard. Beat egg whites until stiff, gradually adding sugar; gently fold into custard mixture. Tear angel food cake into bite- sized pieces. Place pieces in well-oiled 9 x 13-inch pan and pour custard over all. Chill until firm. Serves 6