Fill a medium saucepan with a few inches of water and bring it to a simmer over medium heat. Place a heatproof mixing bowl over the saucepan, ensuring it doesn’t touch the water.
In the mixing bowl, combine egg whites, sugar, water, cream of tartar, and salt. Using a hand mixer, beat the ingredients on low speed for about a minute until combined.
Increase the speed to high and beat for 7 minutes until the mixture becomes glossy and forms stiff peaks. The frosting should hold its shape when the beaters are lifted.
Remove the bowl from heat and mix in the vanilla extract. Continue beating for another minute until the frosting is smooth and thick.
Let the frosting cool slightly before using. Spread over cakes, cupcakes, or brownies for a light and fluffy finish. Try it with Chocolate Chip Cookie for an extra sweet treat!