In the heatproof bowl of an electric mixer set over a saucepan of simmering water, combine sugar, corn syrup, 1/4 cup water, and egg whites. Cook over medium heat, stirring frequently, until mixture registers 160 degrees on an instant-read thermometer, about 2 minutes.Advertisement
Attach bowl to a mixer fitted with the whisk attachment. Beat mixture on high speed until glossy and voluminous, about 5 minutes. Beat in vanilla. Use immediately.