Swiss Meringue Buttercream for Cupcakes

1 . Stage

Place sugar and egg whites in the heat-proof bowl of an electric mixer. Set bowl over a pan of gently simmering water, and whisk until sugar has dissolved and egg whites are hot to the touch, about 3 minutes. Test by rubbing the mixture between your fingers; it should feel completely smooth.

2 . Stage

Transfer bowl to mixer stand. Using the whisk attachment, beat on high speed until mixture has cooled completely and formed stiff and glossy peaks, about 10 minutes.

3 . Stage

Add the butter, one piece at a time, and beat until incorporated after each addition. Don't worry if the buttercream appears curdled after all the butter has been added; it will become smooth again with continued beating. Add vanilla and beat just until combined.

4 . Stage

Switch to the paddle attachment, and beat on the lowest speed to eliminate any air pockets, about 5 minutes. If using buttercream within several hours, cover bowl with plastic wrap, and set aside at room temperature in a cool environment. Or transfer to an airtight container and store in the refrigerator, up to 3 days. Before using, bring buttercream to room temperature and beat on the lowest speed with the paddle attachment until smooth, about 5 minutes.