In a large stainless steel or glass bowl, combine skim milk, buttermilk, rennet, and salt. Cover lightly with plastic wrap and leave out on kitchen counter at room temperature for 18 to 24 hours. You will then find one large cheese curd floating in whey. Use a slotted spoon to fill molds with the cheese. Discard the whey. Place molds on a rack in a roasting pan (so cheeses can drain) and cover lightly with plastic wrap. Refrigerate for 6 to 8 hours. Turn cheese out of molds and store in a tightly covered container for up to two weeks. Photo credit: Evgeny Karandaev/Shutterstock.