You can spoon or brush Royal Icing onto cookies, but for the cleanest look, try the flooding technique. Using a piping bag fitted with a narrow tip, pipe a rim around the edge and the hanging hole. (If icing is too thick, stir in water 1/4 teaspoon at a time. If it is too thin, stir in powdered sugar.) Let stand until set. Using icing that has been thinned until it drips off a spoon, flood the center of the cookie. (A squeeze bottle or paintbrush works great for flooding. Use a toothpick to spread icing into corners.) Let set again before piping decorations over the base coat. Keep extra icing covered so it doesn't harden.