Meringue Buttercream Frosting

Place sugar, egg whites, and salt in a bowl set over a pot of simmering water. Whisk until sugar dissolves and mixture reaches 160 degrees.

Transfer egg-white mixture to the bowl of a stand mixer fitted with the whisk attachment, and beat on medium speed 5 minutes. Increase speed to medium-high, and beat until stiff, glossy peaks form and meringue has cooled, about 6 minutes. Reduce speed to medium, and add butter, 1 piece at a time, beating well after each addition. Beat in vanilla. Use immediately. Or refrigerate, covered, up to 3 days; bring to room temperature, and beat with a mixer on low speed until smooth before using.