Pretty cookies can't exist without icing. Sure, plain, undecorated cookies are nice and taste great, but adding even just that one coat of royal icing takes the experience from tasty to sugar fantasy.
Send your cookies out with a nice set of new clothes by watching this cake decorating video on how to make meringue powder buttercream icing. The buttercream part means this icing will be smooth, rich, and sweet.
This recipe also turns into glaze very nicely with a few drops of water.