4 ounces egg whites

8 ounces sugar

1 ounce corn syrup

10 ounces (2 ½ sticks) unsalted butter, at room temperature

 

Whisk together the egg whites, sugar, and corn syrup in the bowl of a stand mixer. Place the bowl over a medium pan of simmering water, and heat, whisking constantly, until an instant-read thermometer registers 141˚F. In a mixer fitted with a whip attachment, whip the egg white mixture on high until cooled to room temperature. With the motor running on high, add the butter a tablespoon at a time, whipping for a few seconds after each addition until just combined, and stopping the mixer once or twice to scrape down the sides of the bowl. Continue to whip on high until light and fluffy.

 

Makes more than enough to frost a layer cake or 2 dozen cupcakes. You can flavor this buttercream however you like. For vanilla buttercream, beat in 1 ½ teaspoons vanilla extract. For chocolate buttercream, beat in 1 teaspoon vanilla extract plus 5 ounces chopped semisweet chocolate or 2/3 cup semisweet chocolate chips, melted and cooled slightly. Buttercream keeps for about a week tightly sealed in the refrigerator. Bring to room temperature and rewhip until light and fluffy before using.