Use this to make our Coconut Chick Cupcakes.
Pulse vanilla seeds and sugar in a food processor. Pour through a sieve into a bowl; discard large pieces of bean.
Put vanilla-sugar mixture, egg whites, and salt in a heatproof mixing bowl set over a pan of simmering water. Heat, whisking constantly, until sugar is dissolved and mixture registers 160 degrees on an instant-read thermometer.
Transfer bowl to an electric mixer fitted with the whisk attachment. Beat on medium speed 5 minutes. Raise speed to medium-high; beat until stiff peaks form and mixture is glossy and cooled.
Reduce speed to medium; beat in the butter, 1 piece at a time. Beat in extract.