This truly is the best ever sugar cookie icing! It hardens without becoming too crunchy, is full of vanilla flavor, and can be colored to suit any holiday.
Make the outline icing by combining the powdered sugar, 5 tablespoons of milk, corn syrup, and vanilla extract. Mix in the food coloring, transfer part of the icing to another bowl, and set aside.
Outline each cookie with the outline icing, then use the flood icing to fill in the cookie. Use a toothpick to move the icing around and fill any empty spots.