This recipe was clipped from what could be a promo recipe folder (maybe by Betty Crocker), date unknown. Recipe is typed below along with a scanned copy.
QUICK FUDGE ICING
Mix in saucepan 1 cup sugar and 1/4 cup cocoa. Add 1/4 cup butter, 1/2 cup milk, 2 tbsp. white corn syrup, 1/8 tsp. salt. Stir and bring to a full rolling boil. Boil vigorously, stirring occasionally, for 3 minutes. (Cocoa syrup must become thick and coat the spoon, so be sure that the mixture boils hard.) Cool. Beat in 1 1/2 to 2 cups sifted confectioners’ sugar and 1 tsp. vanilla. Let stand until icing is of spreading consistency.
NOTE: Cocoa syrup may be cooled quickly in ice water before adding confectioners’ sugar and vanilla.