In a medium-sized mixing bowl, combine powdered sugar, corn syrup, vanilla, and 2 Tablespoons of the milk.

If the frosting is too thick, add more milk (1 teaspoon at a time) until Icing is smooth and drizzles in a smooth ribbon from the whisk. To test consistency, drizzle the icing back and forth in the bowl. The ribbon that you drizzle should hold its shape for several seconds before dissolving back into the icing in the bowl. If the frosting is too thin, add more powdered sugar until you reach the right consistency.

Divide the frosting into bowls and add food coloring as desired.

Portion the frosting into a piping bag fitted with a tip (I like Wilton 4 or 5) or a ziploc bag with the corner snipped off. If using a ziploc, make sure your frosting is thin enough that it won't break open the bag when squeezed.

Frost cookies and decorate with additional sprinkles or candies if desired.

Let the frosting harden completely before stacking and storing; this can take several hours depending on how thick/thin your frosting is and the humidity in your home. I like to leave my cookies out overnight to harden.