I have checked a few powdered sugar brands and they all have cornstarch in them. Domino does, all the store brands I've checked do too. I tried to make my own on two separate occasions, once with a food processor and once with a blender...neither (I thought) were powdery enough to be reliable. I am currently using a store brand that has cornstarch in it.
Does anybody know of a brand that does not have cornstarch?