Everytime I make a buttercream (with 1/2 shortening, 1/2 butter, sugar, vanilla, milk or corn syrup to thin) it crusts, which I know is exactly what it's supposed to do.  However, when I go to a bakery and order a cupcake with buttercream frosting, the frosting is not crunchy.

I'm confused.  Is the bakery buttercream somehow different than mine?  I use the Wilton recipe.

I can't help much with this but it sounds like they use a different ratio in the ingredients. Perhaps more butter than shortening, or less sugar and more syrup? Or maybe, they use something that comes ready-made and just color it.

AIf it isn't crusting, they are doing something different than you are. Perhaps using all butter, perhaps making a meringue-based icing. I personally could never get ABC made with Crisco to crust due to the lack of trans fats. When I make ABC with the store brand shortening, however, it has a definite crust and that crunch you spoke of.

Do you like the crunch or are you looking to get away from it?

What makes a b'cream crust is the amount of fat vs. the amount of sugar.

The more fat the less it will crust.

The best ratio is 2 cups of fat (be it butter, shortening or a combination) to 2# of sugar.

Sooooo, yes, the bakery is using a different ratio in the icing they make/use.  It may be *almost* the same, just using more fat or it could be totally different.