Use this to make our Gingerbread Town-Square Cake. This frosting sets quickly, so make it just before you're ready to use it.
Bring 1 1/2 cups sugar, the corn syrup, and water to a boil, stirring until sugar has dissolved. Clip a candy thermometer to side of pan. Continue to cook, without stirring but washing down sides of pan with a wet pastry brush to prevent crystals from forming, until mixture reaches 230 degrees, about 5 minutes. Remove from heat.
Meanwhile, with a standing mixer fitted with the whisk attachment, beat egg whites on medium speed until soft peaks form. Gradually beat in remaining 1/4 cup sugar, 1 tablespoon at a time.
Reduce speed to medium-low, and pour syrup in a slow, steady stream down side of bowl. Raise speed to high, and beat until thick, shiny, and cooled, about 7 minutes. Use immediately.