Combine the egg whites, sugar, water and cream of tartar in the top of a double boiler. Mix thoroughly.
Place over boiling water and beat constantly until the mixture holds a peak. This will take at least 7 minutes, but most likely closer to 10 minutes.
Remove from the heat.
Add vanilla and beat until thick enough to spread.
Makes 5-6 cups of frosting.
The calories shown are based on the recipe making 5 cups of frosting, with 1 serving being 1/3 cup. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate. **We are not dietitians and recommend you seek a nutritionist for exact nutritional information. The information in the nutrition box are calculated through a program and there is room for error. If you need an accurate count, I recommend running the ingredients through your favorite nutrition calculator.**