In a small saucepan over medium-high heat, bring sugar and water to a boil, stirring frequently. Decrease heat to low and simmer for an additional 5–7 minutes. Dip a pastry brush in water and run along the sides of the pan to dissolve any crystals forming along the sides.

In the bowl of a stand mixer fitted with the whisk attachment, beat the egg whites with the cream of tartar and salt until stiff peaks form.

While on medium-low speed, carefully drizzle the hot syrup into the egg whites. Then whisk continuously about 5 minutes on high until blended.