This recipe is light and fresh, no one will know butter is the main ingredient. No competition with store bought frosting.
Bring the water and sugar to a boil in a heavy 1-1/2 quart saucepan, making sure to brush down any sugar that is on the side of the pan. Do not stir. You can put a lid on the pot to speed the dissolving of the sugar. Boil syrup until reaches 238F on a candy thermometer.
While syrup is boiling, in the bowl of a mixer, beat whites with a pinch of salt until foamy. Add cream of tartar. Beat whites until soft peaks and add hot syrup in a stream down the side of the bowl, beating the whole time. The syrup mixture has to hit the side of the bowl before hitting the eggs or else it will cook the eggs. Beat mixture on high until completely cool, 5-10 minutes.
Beat in butter 1 tablespoon at a time until the mixture is thick and smooth. Add vanilla and beat until incorporated.
Frosts one 9 inch thriple layer cake.
Chocolate: Add 3 oz melted chocolate at the very end after the vanilla.
Mocha: 2-1/2 TBS instant espresso powder dissolved in 1 TBS hot water, add espresso mixture after the butter, omit the vanilla. Add chocolate as above, and 1/4 tsp salt. Beat until smooth.
1/2 cup water
1 cup sugar
4 egg whites
Pinch of salt
1/4 tsp cream of tartar
2 cups unsalted butter at room temperature
1 tsp vanilla