This matured, thickened cream has a slightly tangy, nutty flavor and velvety rich texture. The thickness of crème fraîche can range from that of commercial sour cream to almost as solid as room-temperature margarine. In France, where crème fraîche is a specialty, the cream is unpasteurized and therefore contains the bacteria necessary to thicken it naturally. In America, where all commercial cream is pasteurized, the fermenting agents necessary for crème fraîche can be obtained by adding buttermilk or sour cream. A very expensive American facsimile of crème fraîche is sold in some gourmet markets. The expense seems frivolous, however, when it's so easy to make an equally delicious version at home. To do so, combine 1 cup whipping cream and 2 tablespoons buttermilk in a glass container. Cover and let stand at room temperature (about 70°F) from 8 to 24 hours, or until very thick. Stir well before covering and refrigerate up to 10 days. Crème fraîche is the ideal addition for sauces or soups because it can be boiled without curdling. It's delicious spooned over fresh fruit or other desserts such as warm cobblers or puddings.