Icing for Gingerbread Houses

4 egg whites, at room temperature
1/4 tsp. cream of tartar
4 tsp. water
6 cups powdered sugar
food coloring, optional

1.  Beat the egg whites, cream of tartar, and water together until foamy; gradually add the 6 cups powdered sugar.

2.  Beat for 5-6 minutes or until a butter knife can stand upright in frosting.  Add food coloring if desired.

 Use for making gingerbread houses.  Dries very hard.