Small batch (will generously frost 12-15 cupcakes)
1poundunsalted buttercubed, softened (room temperature works too, but takes longer to come together)
3teaspoonsclear vanilla extract
Large batch (will generously frost 24-30 cupcakes)
2 1/2lbs.unsalted buttersoftened
1tbspclear vanilla extract
Set a saucepan filled one-third full of water over medium-high heat and bring to a simmer.
Whisk together the egg whites, sugar, and salt in a large heatproof bowl ( I suggest a stainless bowl). Set over the simmering water and whisk until the mixture is hot to the touch and the sugar has dissolved (120-140 degrees on a candy thermometer, to be sure).
Transfer the mixture to the bowl of a stand mixer fitted with the whisk attachment.
Beat on low speed for 2 minutes. Increase to medium-high until stiff peaks are formed.
Continue beating at medium-high speed until the mixture is fluffy and has cooled (the mixing bowl should feel cool to the touch).
Turn the mixer off and switch from the whisk attachment to the paddle. Turn the mixer on medium-low and add the butter, a few cubes at a time, beating until well incorporated before the next addition.
Add the vanilla extract. Divide batter and tint with food coloring, if desired.
Beat until the frosting is thick and completely smooth.
Store in an airtight container until ready for use.