Prepare Double Boiler: Begin by setting up a double boiler. Fill the bottom pot with an inch or two of water, making sure the water doesn’t touch the top pot. Bring the water to a simmer.

Combine Ingredients: In the top pot of the double boiler, combine sugar, water, corn syrup, egg whites, and cream of tartar.

Beat Over Simmering Water: Place the top pot over the simmering water and beat the mixture with a handheld electric mixer on medium speed. Ensure that the beaters reach the bottom of the pot to prevent the egg whites from cooking.

Continue Beating: Continue beating for approximately 7 minutes or until stiff peaks form. The mixture should be glossy and smooth.

Add Vanilla: In the final moments of beating, add the vanilla extract and beat for an additional 30 seconds to incorporate.

Remove from Heat: Once the frosting is ready, remove the pot from the heat.

Cool and Frost: Allow the frosting to cool slightly, then use it to frost your cake or cupcakes immediately. The frosting sets quickly, so works efficiently.