Using a fork, stir the confectioners' sugar, vanilla, corn syrup, 4.5 Tablespoons (67ml) of water, and salt together in a medium bowl
Switch to a whisk and whisk in ½ Tablespoon (8ml) of water
Lift the whisk and let the icing drizzle back into the bowl - the ribbon should hold shape for a few seconds before melting back into the icing
If too thick, whisk in another ½ Tablespoon (8ml) of water or more until reaching target consistency
Stir in gel food coloring if desired, using 1-2 drops at first and adding more as needed
Spoon icing into squeeze bottles or piping bags fitted with Wilton Piping Tip #4
Outline cookies with icing first, then fill in/flood the middle
Add sprinkles right after applying icing if desired
Allow icing to dry for 24 hours
