- Combine the egg whites and sugar in a heat-proof bowl.
- Set the bowl over a pan of simmering water. Stir the mixture until the egg whites have warmed and the sugar is dissolved—rub a bit of the mixture between your fingers to make sure there are no grains of sugar left. Be careful not to let the egg whites cook.
- Remove the egg whites from the heat, and whip them into a stiff-peaked meringue.
- With the mixer running on medium-high, gradually add the chunks of butter. Wait until the previous piece is incorporated before adding the next one.
- Beat in any desired flavorings.
- Use buttercream as desired.
Notes, tips, and variations
- If the butter is cold, it will not properly incorporate into the frosting.
- The mixture may look like it is curdling partway through the butter addition—continue beating, and the mixture should come together.