Ingredients
1 1/2 cups sugar
5 large egg whites
Pinch of cream of tartar
1 pound unsalted butter, cut into small pieces (4 sticks)
1 teaspoon pure vanilla extract
Preparation
In a small saucepan over medium heat, bring sugar and 1/3 cup water to a boil. Boil until syrup reaches soft-ball stage (238 degrees.on a candy thermometer).
In an electric mixer fitted with the whisk attachment, beat egg whites with an electric mixer on low until foamy. Add cream of tartar; beat on medium high until stiff but not dry.
With mixer running, pour syrup down side of bowl into egg whites in a steady stream, and beat on high speed until steam is no longer visible, about 3 minutes. Beat in butter a few pieces at a time. Add vanilla and beat until smooth. If it looks curdled at any point, keep beating to smooth out.
