Place egg white in bowl of standing mixer fitted with whisk attachment, and set aside; measure sugar, and set 3 teaspoons aside.
Combine remaining sugar and the corn syrup in medium saucepan with 1/4 cup of water, and bring to a boil over medium heat, stirring to combine; cook syrup without stirring until it reaches 240 degrees, using a candy thermometer.
As sugar cooks, pour 3/8 cup cold water into small saucepan, and sprinkle gelatin on it; let stand 5 minutes; put pan over burner on very low heat, and stir to dissolve; leave pan on warm burner.
Just before sugar syrup reaches 240 degrees, beat egg white on low speed until foamy; add 1 teaspoon of reserved sugar and the salt; increase the heat to high, and continue beating, sprinkling with remaining 2 teaspoons until medium-stiff peaks have formed; with mixer running, pour syrup into egg white; beat on high speed 2 minutes; add dissolved gelatin; beat until fluffy and cool, about 5 minutes; add vanilla.
Sauce will hold at room temperature for 4 hours; after refrigeration, sauce may be heated over a double boiler until lukewarm, and beaten in a standing mixer until fluffy.