I do cake decorating and the recipe I use is as follows (it usually does have that thin crust that Patty was looking for):

Cream the shortening and flavorings together. Then add the sugar, a little at a time, until the mixture begins to look like coarse crumbs. Then add salt water a little at a time until the mixture begins to get smooth and becomes the consistency of icing.

Cake decorators generally like their icing on the stiff side, but it is a matter of personal taste. Add the salt water until it is the consistency you want.

After you ice the cake, and it sits for a couple of hours, it should have that "micro-thin" crust your looking for.

As a personal side note, I usually add more liquid vanilla flavoring and butter flavoring to my icing, because I want the taste, not the terrible sweetness of some icings. Almond extract can also be used in place of the vanilla, if you want to try something a little different. If you do use almond, I'd use less than the vanilla, because it tends to be a stronger flavoring.

know) only by cake decorators. Every cake decorating store that I have been in has it in stock. I'm not really sure of the significance of it on the whole, perhaps Wilton could answer that. I do know that if you add more than what the recipe calls for, it makes your icing bitter. I have run out of it before and can certainly tell the difference.