If you're following keto, this list of keto-approved cheeses is one you should check out. If you're not worried about keto, just worried about this recipe working out, then any sliced cheese will do. Cheddar, provolone, Munster, Colby Jack ... any of them will work. The thinner the cheese, the less it will spread as it bakes. So if you're getting cheese sliced at a deli counter, ask for it to be cut as thin as possible. But, packaged cheese is just fine too. The ones that come as a block separated by tiny parchment paper sheets is better than individually wrapped slices, mostly because the former tends to have less preservatives and will bake better because of that. You can slice your own cheese, if you want, but make sure to slice thin, uniformed pieces if you do so that the cheese will bake evenly. And, if you want, you can use dollops of Parmesan cheese to make these too. The very finely grated, basically powdered form, of Parmesan cheese won't work, though. You need a thick grated Parmesan cheese to make a homemade Parmesan crisp. We don't suggest using shredded cheese, since the preservatives in shredded cheese don't allow it to melt as well. But if you don't have sliced cheese, shredding a block of cheese will work in a pinch.