Prepare the Syrup: In a small saucepan, combine the sugar, corn syrup, and water. Heat the mixture over medium heat, stirring occasionally, until the sugar dissolves completely.

Whip the Egg Whites: While the syrup is heating, place the egg whites in a clean mixing bowl. Beat them with an electric mixer on medium speed until soft peaks form.

Combine and Whip: Slowly pour the hot syrup into the egg whites in a thin, steady stream while continuing to beat on medium speed. This step requires caution to avoid splattering. Once all the syrup is incorporated, increase the mixer speed to high and whip until the mixture is glossy, stiff, and slightly cooled. This usually takes about 7-10 minutes.

Add Flavoring: If desired, mix in vanilla extract or any additional flavorings during the last minute of whipping.

Store:Transfer the marshmallow fluff to an airtight container and store it in the refrigerator for up to two weeks.