NOTE: How to Make Creme Fraiche at Home: In a medium jar, stir together 1 cup of heavy, 35% whipping cream (not ultra-pasteurized) and 1 Tbsp. buttermilk. Set a lid on top, but don't twist to seal it (to allow air to escape, but to keep dust and things out). Set on your counter or window sill for 12-24 hours, or until the mixture resembles stirred sour cream. The time it takes to that point will vary depending on the temperature of your room. Mine took about 20 hours. At that point stir the mixture well, then transfer to the fridge, again, topping with a lid but not twisting to seal it, as it will continue to process). Refrigerate a further 6 hours or longer, or until it is the consistency of cream cheese.