- 3 1/2 cups sugar
- 14 large egg whites, or packaged whipping-quality egg whites
- 4 1/2 cups (9 sticks) unsalted butter, softened, cut into tablespoons
- 2 teaspoons pure vanilla extract
- In a heatproof mixing bowl set over a pot of simmering water, whisk together the sugar and egg whites until sugar has dissolved and mixture is warm, 2 to 3 minutes. Remove bowl from heat.
- Using an electric mixer, beat egg-white mixture on high speed until fluffy and completely cooled, about 10 minutes.
- With mixer on low speed, add the butter, a tablespoon at a time, beating until fully incorporated after each addition. (Don't worry if your buttercream appears curdled after all the butter has been added; continue beating until smooth again.)
- Add the vanilla extract, and beat until combined. If using buttercream the same day, let stand at room temperature, covered tightly with plastic wrap. When tinting buttercream, add food coloring a drop at a time, and stir well before adding more.
Transfer buttercream to an airtight container, and refrigerate up to 5 days; before using, bring to room temperature, and beat until smooth, about 10 minutes. Do not tint before storing, as color tends to fade.