I made a batch of cookies last night using a recipe I've made before, with terrific results (Cooks Illustrated thick and chewy chocolate chip cookies). But, they turned out terribly, and I can't figure out why. They didn't spread very much, and they were much harder (not to mention more tasteless) than they should have been. I used a professional cookie sheet (one from william-sonoma - pretty heavy and thick), and I am wondering if this has something to do with it. I also didn't use parchment paper (the recipe called for it, but I didn't have any on hand). Does the type of cookie sheet (or lack of parchment) make that much of a difference?