this is actually cc's recipes for royal icing that i've used to decorate cookies with:
-Royal Icing Using Meringue Powder:
4 cups (440 grams) confectioners' (powdered or icing) sugar 3 tablespoons (30 grams) meringue powder (can be found at stores that carry cake decorating supplies) 1/2 teaspoon extract (vanilla, lemon, almond) (optional) 1/2 - 3/4 cup (120 - 180 ml) warm water
In bowl of electric mixer beat the confectioners sugar and meringue powder to combine. Add the water and beat at low to medium speed until desired consistency (about 5-7 minutes).
To keep icing soft and shiny add a few drops of glycerin. Color icing using gel pastes by dipping the tip of a toothpick into the food coloring and then mixing it into the icing.
The icing needs to be used immediately or transferred to an airtight container as royal icing hardens when exposed to air. Cover when not in use.