4 large egg whites
1 1/4 C granulated sugar
1 T light corn syrup
1/4 tsp cream of tartar
pinch of salt
1 tsp vanilla extract
1. Make frosting: Put egg whites, sugar, cream of tartar and salt in a large, clean metal bowl set over a saucepan of barely simmering water. Whisk constantly but gently until the mixture reaches 130 degrees, 7-9 minutes.
2. Transfer the bowl to the mixer. Beat the mixture on low speed for 2 minutes, then increase the speed to medium and beat for 2 more minutes. Increase the speed to high and beat until it is very thick and glossy about 5 minutes. Add the vanilla and beat well.
3. The frosting is best used right away, but will keep covered at room temperature for up to one hour.
Note: Be sure your sugar-egg white mixture is hot enough to dissolve all the sugar granules, or you will end up with grainy frosting.
From: The Sweetapolita Bakebook