All hail the supreme cake icing: Swiss Meringue Buttercream! Learn to make it like a pro with these buttercream basics and 3 tips if the icing goes berserk!
In the top of the double boiler, over gently simmering water, whisk together sugar, salt and egg whites. Heat, whisking constantly, until sugar is dissolved and the mixture reaches 140F (60C) or is uncomfortably hot to the touch.
Pour egg mixture into a stand mixer bowl (with whisk attachment) and beat on medium speed until soft peaks form and the mixture is cooled to room temperature. beat in vanilla.
Meanwhile (with paddle attachment), cut butter into small cubes, about 1/4 inch (5 mm) in size,
Add butter cubes to the cooled egg mixture, two or three at a time, beating until all of the butter is incorporated and the icing is smooth and satiny.
Use immediately or cover with plastic wrap directly on the surface and store at a cool room temperature for up to 24 hours.