cup unsalted butter, softened
In a small mixer bowl combine sugar and egg whites. Place over simmering water. Do not let water go higher than 120 degrees. Whisk whites until sugar is dissolved; remove from heat. Beat at high speed until stiff peaks form and mixture has cooled. Using medium speed gradually beat in butter and vanilla. Continue beating until mixture is smooth and fluffy. Tip: Because of food safety, only pasteurized eggs should be used in recipes where the eggs are not cooked.