In a heatproof bowl, add the egg whites, sugar, and cream of tartar. Place the bowl on top of a medium pot with about 2 inches of simmering water.
Whisk the mixture consistently until the sugar has dissolved, about 5 minutes. The mixture will become frothy, and you’ll know it’s ready when the thermometer reads 160 degrees. It may take another 2 minutes to reach that temperature.
Add the frothy egg mixture into a stand mixer bowl and add the vanilla extract.
Mix on high for 5 minutes. Time to enjoy!