combine egg whites, sugar, cream of tarter, and water in the top of a double boiler. Beat on high speed for 1 minute with mixer. Place overboiling water (water should not touch bottom of upper pan). Beat on high speed 7 minutes. Remove pan from boiling water, add vanilla. Beat for 2 more minutes. this frosts a 13 x 9 inch pan.
Not a NESTLÉ®-tested recipe.