In the heatproof bowl of a stand mixer, whisk together sugar and egg whites by hand. Place bowl over a saucepan of simmering water. Cook, whisking frequently, until sugar completely dissolves and an instant-read thermometer registers 120°F (49°C) to 130°F (54°C).

Carefully return bowl to stand mixer. Using the whisk attachment, beat at high speed until stiff peaks form and bowl is cool to the touch, 2 to 3 minutes. Use immediately.