In the heatproof bowl of a stand mixer, whisk together sugar, egg whites, cream of tartar, and salt. Place over a saucepan of simmering water, and cook, stirring frequently, until an instant-read thermometer registers 160°F (71°C), 15 to 20 minutes.

Return bowl to stand mixer. Using the whisk attachment, beat sugar mixture at medium-high speed until bowl is room temperature and meringue forms glossy, stiff peaks, about 10 minutes. Beat in vanilla bean paste. Use immediately.