In a large bowl, combine sifted powdered sugar, 3 Tbsp milk, and light corn syrup. Whisk until smooth. If mixture is too dry, add additional milk, one teaspoon at a time until mixture can be stirred.
Stir in extracts.
Glaze should be thick, to test that is its the right consistency drop a few droplets on top of a test cookie. If the glaze remains stiff, it needs to be thinned. If it runs off the cookie, it is too thin and needs more powdered sugar. If it settles down smoothly, it is just right.
Divide glaze into four small bowls.
Working with one bowl at a time, use a toothpick (a different toothpick for each color) and dip it into the food coloring bottle and then into the glaze. You want a small dot of food coloring. (see video up in post)
Drag a toothpick through the food coloring and glaze until it is prettily swirled/marbled.
Holding your cookie at the base, dip the surface of each cookie into the glaze (take a look at your first cookie --- are you satisfied with the pattern? Adjust whorls with additional food coloring as needed.
If you are going to add sprinkles, add them right after glazing to ensure they sticks to the glaze before it dries.
Once the first bowl runs out or the colors become too muddled together from dipping, moe onto your next bowl of food coloring (you will probably need to stir first before adding your coloring, as the surface may have begun to harden).
Repeat steps of adding coloring with toothpicks to glaze in bowl until all cookies have been dipped. Allow them to harden at least 30 minutes (may take longer) for glaze to set. Enjoy!
Keep uneaten cookies in an airtight container at room temperature.