Dissolve 2½ c. sugar, ⅛ tsp. salt and ⅓ c. dark corn syrup in ⅔ c. water. Cook until mixture reaches boiling point. Meanwhile, beat 2 egg whites until foamy. Pour 3 tblsp. sugar mixture into egg whites; continue beating eggs until stiff but not dry. Add 1 tsp. vanilla. Boil syrup mixture to 240° on candy thermometer, or until it spins a thread at least 10" long when dropped from edge of spoon. Then pour syrup slowly over egg whites, beating until frosting is thick, cool and of good spreading consistency. Spread over cake. If the frosting becomes hard, add a drop or two of hot water to the mixture. This frosting does not form a crust that cracks when cake is cut.