See below

In top of boiler not over heat, combine 1 1/2 cups sugar, 2 unbeaten
egg whites, 2 tsp. light corn syrup & dash of salt. Add 1/3 cup cold
water. Beat 1/2 minute at low speed of electric mixer to blend. Place
over boiling water (upper pan should not touch water). Beating
constantly with electric mixer, cook about 7 minutes or till frosting
forms stiff peaks. Remove from heat & add 1 tsp. vanilla. Beat about
2 minutes more or till of spreading consistency. Spread on cake at
once.