Combine sugar, egg white (at room temperature), corn syrup, and salt in top of a large double boiler; add cold water, and beat on low speed of electric mixer for 30 seconds or just until blended.
Place over boiling water; beat on high speed of electric mixer about 7 minutes or until stiff peaks form. Remove from heat, and place over cold water; let stand about 5 minutes. Stir in vanilla. Spoon warm frosting on cooled cake.