This is a tip I picked up from Ina Garten. If you have the rind left after using up a chunk of Parmesan cheese, save it in a zip-top bag in your freezer. It can be added to soups, stews, and pasta sauces as they cook. The rind contains salt, fat, acid, and even that elusive 5th sense of taste, umami. As the soup cooks, the rind softens and infuses the liquid with all those components. Primarily, it will add a salty flavor and thicken the soup.