Combine all of the ingredients except the vanilla in a stainless steel heavy-bottomed saucepan.
1 cup sugar, ¼ teaspoon salt, ½ teaspoon cream of tartar, 2 Egg whites, 3 tablespoons water
Place mixture over medium-low heat and beat with an electric hand mixer constantly for 5-7 minutes, or until icing is fluffy and stiff peaks form when the beaters are removed.
Remove from heat and stir in the vanilla. Ice the cooled cake.
1 teaspoon vanilla extract
Notes
You'll need two recipes of this icing to ice a layer cake. Fortunately, this recipe doubles beautifully, so there's no need to make two separate batches, just double it and make it all at once.
If you want to jazz up your frosting, here are some fun additions:
Use brown sugar instead of white sugar.
Fold about 3 ounces of melted chocolate chips into the finished frosting. You want both products to be at the same temperature.
Use a different extract flavor rather than vanilla, like peppermint or almond extract.
You can also torch the frosting like you would meringue.