You can use this icing for both the glaze and the detailing! This recipe makes enough to glaze about 24 cookies. You cannot mess it up. I repeat, you cannot mess it up. Add more or less powdered sugar to change consistency, based on application!
Sift your powdered sugar to make sure it is smooth and fine for the mixing of your icing!
Once your powdered sugar has been sifted, mix in the vanilla and milk with a wisk until it is smooth.
Glaze: Use the recipe above +1 - 2 T of milk. Your icing should be runny. You can put the glaze on a shallow plate with a lip or in a shallow bowl that is wide enough for dipping your cookies. All you do is hold your cookie & dip the front into the glaze. Then set to dry, on a cooling rack set on top of a jelly roll pan or parchment paper.
Detailing: Use the same recipe above and your icing should be thick. Thick enough to hold shape & not drip out of your icing bag but not too thick, where you can't pipe it through a size 3 or 4 icing tip.