Ingredients

1 1/4 c water
5 large egg whites
Pinch of cream of tartar
1 lb (4 sticks) cold unsalted butter, cut into small pieces
1 tsp. vanilla extract

Directions

In small saucepan over med. heat, bring sugar and 1/3 C water to a boil. Boil until syrup reaches soft-ball stage (238 deg. on a candy thermometer).

In the bowl of an electric mixer, use the whisk attachment to beat egg whites on low speed until foamy. Add cream of tartar and beat on med. high speed until stiff but not dry.

With the mixer running, pour the sugar syrup into egg whites in a steady stream and beat on high speed until steam is no longer visible, about 3 minutes. Beat in butter, piece by piece. Add vanilla and beat for 3 to 5 minutes, until frosting is smooth and spreadable. If it looks curdled at any point during the beating
process, keep beating to smooth it out. If it becomes too soft for piping, stir over ice water to stiffen. (This buttercream holds its shape particularly well, making it good for decorating.)