In 1-quart saucepan, heat chocolate chips and shortening over low heat, stirring frequently, until melted; set aside. For glaze, mix powdered sugar, 1/4 teaspoon peppermint extract, 1 to 2 drops food color, the corn syrup and enough of the 3 to 4 teaspoons water to make a thick glaze that can be easily drizzled. Drizzle over cake. Immediately spoon melted chocolate over glaze in 1/2-inch-wide ring. Working quickly, pull toothpick through chocolate to make swirls. Refrigerate until serving time. Store loosely covered in refrigerator.