This is the best "homemade recipe I have run across for icing cookies...because it hardens and it's shiny...I got the recipe from a Wilton book, and it's one of my favorites..

Cookie Icing Recipe
This icing dries to a shiny. hard finish and tastes good too. Great to use for icing or to outline and fill in with a tip #2 or 3..

1 cup sifted confectioners sugar
2 tsp. milk
2 tsp. light corn syrup

Place sugar and milk in bowl. Stir until mixed thoroughly. Add corn syrup and mix well. For filling in areas, use thinned icing (add small amounts of light corn syrup until desired consistency is reached)

P.S. I always add vanilla flavoring to this recipe

Also...
I tried something different this past Christmas when all my (8) grandchildren were decorating cookies at the dining room table... I used a whole can of Cream cheese frosting and added a couple tablespoons of corn syrup to the canned frosting and divided it into little souffle cups, (you may have to thin down with milk), and I tinted the small bowls different colors, (this went a long way), as I gave the kids paintbrushes to paint their cookies...All my kids help supervise (and got in the act), and I believe they had more fun than their kids did!! Anyway, most were eaten as they were completed, the kids adored this icing!!Bon appetit!!!