Fill a saucepan with two inches of water and bring it to a boil. Once boiling, reduce the heat to low to maintain a steady simmer. The water will create a gentle heat for your mixing bowl.
In a large, heatproof mixing bowl, combine granulated sugar, water, egg whites, cream of tartar, and a pinch of salt. Using a hand mixer, mix on medium-low speed for about thirty seconds until everything is well combined.
Once combined, place the mixing bowl on top of the saucepan of simmering water, ensuring that the bottom of the bowl does not touch the water. This double boiler method allows for gentle heating to whip the whites properly.
Using the hand mixer, beat on high speed for approximately seven minutes. You'll notice the mixture transform into a thick, glossy frosting that holds stiff peaks. Watch as it becomes fluffy and voluminous.
After seven minutes, remove the bowl from the heat. Add vanilla extract and continue to beat for an additional two minutes. This step enhances the flavor further, making it irresistible.
Now, it’s time to use the frosting! Apply it immediately to your cake or cupcakes. Keep in mind that the frosting will start setting quickly, so work fast!
If you have leftover frosting, store it in the refrigerator covered. It will keep well for up to two days, but be sure to let it return to room temperature before using it again.