The icing that I use for my sugar cookies is called a "Glace Icing" and it also comes from Toba Garrett's class that I took in NYC. There are two parts to this icing method; the outline and the inside or the "flooding" icing. The royal icing is for the dam (or the outline) and the Glace icing is the "flooding" icing. The royal icing should be used immediately - the glace icing can be kept for two weeks in the refrigerator.
Tightly cover the icing if you are not planning to use it immediately and put it in the refrigerator. If you are planning on using it immediately divide the icing into a number of bowls and color as you want. I use plastic squeeze bottles (available online or bakery supply store) with various tips to flood the cookies. This makes application easier. This icing takes 24 hours to dry so some planning is needed for the decorated cookies!
When you have outlined the cookies you are ready to ice. Fill the cookie from the center out with the icing allowing the icing to flood the cookie - do not overfill the cookie; use a toothpick to push the icing to the edge. I place all the cookies that I am going to decorate on a cookie sheet so I do not have to move them after they are iced. As I said it takes 24 hours for the glace icing to dry but it will start to set after one hour. After the icing has hardened (when the icing loses it sheen it is dry) I start to decorate the cookies. You can see the various methods that I use in the photos below. I put colored sugar on the cookies after the icing has set, draw decorations, write names and add dragees. The egg cookie with the purple lines is done in the following manner: ice the cookie with the base color, after one hour run lines of different color icing on the cookie; take a toothpick and drag it alternatively from top to bottom, bottom to top. That will result in the wavy pattern that you see.
Making and decorating these cookies is a wonderful time to gather round with friends and children. During the holidays - all of them - my house is full of friends and their children sitting around the dining room table laughing and creating wonderful memories, both edible and in their hearts. Make a batch of cookies, icing and watch the magic begin!