As I mentioned in my sugar cookie post, Annie's Eats has been a great inspiration to me and my cooking. She has especially fueled my desire to decorate sugar cookies with royal icing. Having never used royal icing, I turned to her tutorial and read through the steps several times before embarking on my first cookie decorating adventure. I highly suggest you check out Annie's tutorial if this is your first time working with royal icing. It is pretty easy to do, although messy, but her tips helped out quite a bit.
Also, I bought the meringue powder at Michael's, using a 40% off coupon. I recommend you do the same; that stuff is pricey!
Source: Annie's Eats
4 cups powdered sugar, sifted
2 tablespoons meringue powder
5 tablespoons water
gel food coloring in desired colors
disposable pastry bags (one per icing color)
1 coupler per bag
1 size 2 or 3 decorating tip per bag
1 squirt bottle per icing color
Combine all ingredients in the bowl of a stand mixer fitted with the paddle attachment.
Mix on low speed until the icing has a matte appearance, about 7-10 minutes. Make sure to scrape down the sides of the bowl to fully incorporate all the powdered sugar.
Transfer the contents of the mixing bowl to an air-tight container. The icing should be stiff, but it will be too stiff to use for decorating. Add a small amount of water at a time (I added about 1/4 of a tablespoon) and stir until fully incorporated. The icing should still be slightly stiff, but be able to be piped. You don't want it to be super thin at this point though.
Mix in the gel icing coloring, a little at a time, until you have reached your desired color.
Fit a disposable pastry bag with a coupler and a size 2 or 3 tip. Using a steady hand, outline each cookie with icing. If you are having any difficulty piping, the icing is still too thick. Add a little more liquid, mix well, and try piping again. Let stand so the icing will set, about one hour (I stuck my outlined cookies in the freezer for about 30 minutes to speed up the hardening process, which worked really well).
Be sure to keep the remaining icing covered to prevent it from hardening.
Once all the cookies have been outlined, squeeze the remaining icing back into the air tight container. Add a small amount of water at a time (about 1/2 a tablespoon) and mix well, to thin the icing. The icing should run off the back of a spoon and completely incorporate back into the rest of the icing in about 5 seconds. Once you think you've added enough water, add a little bit more. If the icing is too thick, it will be difficult to flood and decorate the cookies.
Once the icing has reached the desired consistency, pour it into to a squeeze bottle (or a plastic bag with a hole in one corner), and flood the area surrounded by the piping on each cookie. Carefully spread the icing into the corner with a toothpick.
Allow the cookies to set until the frosting is completely hardened.
Use the remaining to pipe on an additional decorations. If the icing is too thin, add more powdered sugar, mixing well.