Place egg whites and sugar in a bowl that fits over a saucepan well.

Add water to the saucepan and bring the water to a boil, be sure the water does not touch the bottom of the bowl.

Heat the egg whites and sugar until they are hot, the sugar is melted and smooth, not gritty.

Place the mixture in the bowl of a mixer, beat over medium-high until the mixture is no longer hot and it's stiff and shiny. This takes about 10 minutes.

Add in butter one tablespoon at a time beating on medium-high until it's all incorporated and continue mixing until it's a smooth frosting, this takes about 5 minutes.

Mix in vanilla.