In a large bowl, stir together the shortening and corn syrup. Mix in the salt and vanilla flavoring, then gradually mix in the confectioners' sugar until it is a stiff dough. If you are using a stand mixer, use the dough hook attachment. Otherwise, knead by hand. If the dough is sticky, knead in more confectioners' sugar until it is smooth. Store in an airtight container at room temperature or in the refrigerator.
To use, roll out on a clean surface that has been dusted with confectioners' sugar until it is 1/8 inch thick or thinner if you can. Drape over frosted and chilled cakes and smooth the sides down, or cut into strips to make bows and other decorations