"What is creme fraiche? If my local store doesn't carry it, is there a good substitute, or can I make it at home?"
Creme fraiche is a sweet and slightly sour, nutty substance about the thickness of sour cream. It was traditionally made from unpasteurized cream left at room temperature. You can buy pasteurized versions in many grocery stores: it is sold in the dairy or cheese sections in little plastic tubs.
You can also make your own creme fraiche: combine two parts lukewarm heavy cream with one part buttermilk. Leave it on the counter partially covered overnight, and in the morning it will be somewhat thickened and have a pleasant nutty flavor. Refrigerate and use it within a week. Store-bought creme fraiche keeps longer, and is stamped with a use-by date.
Creme fraiche is used to thicken and add creaminess to soups, stews and sauces, and is used as a topping on appetizers, desserts and fruit. It is especially delicious whipped with a little confectioners' sugar and served over a warm fruit crisp.