In a small saucepan, cook sugar and water over medium-high heat until a candy thermometer registers 240°.

In the bowl of a stand mixer fitted with the whisk attachment, beat egg whites and cream of tartar at high speed until foamy and nearly tripled in volume. With mixer on low speed, add hot sugar mixture in a slow steady stream. Increase speed to high, and beat until meringue is shiny and cool, approximately 6 minutes. Use immediately.