Mix the sugar, corn syrup, and water in a small, heavy saucepan.

Insert a candy thermometer, partially cover pan and bring to a boil over moderate heat.

Remove cover and boil without stirring until the thermometer registers 240-242.

Just before syrup reaches the proper temperature, begin beating egg whites with an electric mixer until soft peaks form.

When syrup reaches the correct temperature, set mixer at high speed and pour syrup into whites in a slow thin stream. Continue beating until glossy and firm enough to hold a shape.

Beat in vanilla.

Makes enough to fill and frost a 9" two layer cake.