Put egg whites, sugar, cream of tartar and salt in a large metal bowl set over a saucepan filled with 1 inch of simmering water (do not let water boil or allow bottom of bowl to touch water).

Adjust heat as needed to maintain a simmer.

Cook over medium low heat, beating with an electric mixer on medium high speed, until frosting holds stiff peaks, about 7 minutes.

Remove bowl from heat, add vanilla and continue to beat until frosting is glossy and poofy, 1 to 2 minutes longer.

*This amount covers the top and the middle of a 2 tiered 9 inch layer cake.*