Add powdered sugar, corn syrup, extracts, and salt to a mixing bowl. You'll need to use a spatula to scoop out all of the corn syrup from the measuring spoon each time - it likes to stick!

Add 3 T of water to the mixture (You'll likely add a little more later, but just start out with 3 tablespoons.)

Stir together using a fork until everything is blended together. Your icing will likely be pretty thick and will need more water, but it's easier to thin icing than it is to thicken it, so that's why I wanted you to start out with less water. To thin it out, add a teaspoon of water, stir, and then evaluate if you need to add more. See the note just below about testing the consistency!

Test the icing consistency: The icing should be thin enough to flow out of a piping bag, but not so thin that it'll run off the cookies. Testing is easy! Just take about a tablespoon of the icing, spoon it in a piping bag or Ziplock-type sandwich bag, cut a small tip out of the bag, and practice on a cookie. You should be able to outline the cookie without the icing running off, and you should be able to fill it in pretty easily. If the icing is too runny, you can add a little bit of powdered sugar - about a tablespoon at a time, mixing between additions - and repeat until it's thick enough.

To color: use gel food coloring (I use Wilton brand), starting with just a small amount, in separate bowls & mixing with the desired amount of white icing. The icing starts to set pretty quickly, so you'll want to cover the main bowl with plastic wrap while you add color + smaller amounts of icing in the other bowls. Transfer to a piping bag soon after you mix in order to prevent the icing from getting too hard in the bowls.

To decorate: Add icing to piping bags or Ziplock sandwich bags, cut the tip out (start out with cutting a smaller tip - you can easily make it larger if you need to), and then use it to pipe an outline around your cookie, and then fill in the inside. You can use the tip to spread the icing around a little bit as you gently squeeze out more icing to fill in the shape. Or, simply drizzle some icing on the cookie for a "scribbled" look. You'll want to add sprinkles right after you ice each cookie, just because the icing does start to set on top pretty quickly.

To dry: Allow cookies to set out overnight - just let them sit on a baking sheet on your counter. (Yes, they'll still taste great the next day!) Unless the icing is very thick, cookies should be dry enough to stack by the morning. If you plan to ship them or transport them in such a way that they'll shift around quite a bit, you may want to give them a few extra hours on top of that to set.