This is simple to make and unlike sour cream, creme fraiche won't separate when you heat it and can be boiled without curdling. Just add 1 tablespoon cultured buttermilk to 2 cups of heavy cream and let it sit at room temperature for 12 to 24 hours, until it thickens. It will be about the consistency of yogurt, but will solidify even more when chilled. Stir well and then store in the refrigerator. It will keep for a week to ten days. You will love having it on hand as a condiment, using it in soups, or sweetening it a bit and using it as a fruit dip.