Add chocolate to milk and place over low flame. Cook until mixture is smooth and blended, stirring constantly. Add sugar, salt, and corn syrup; stir until sugar is dissolved and mixture boils. Continue boiling, without stirring, until a small amount of mixture forms a very soft ball in cold water ( 232 degrees F.). Remove from fire. Add butter and va- nilla. Cool. To lukewarm (110 degrees F.). Beat until of right consistency to spread. If necessary, place over hot water to keep soft while spreading. Makes enough frosting to cover tops and sides of two 9-inch layers, or top and sides of 13x9x2-inch cake. Kate Smith Collection: See Coconut Cake for details.