Crème Fraîche is the French version of sour cream, and it is both tastier and more useful that the sour cream typically found in American grocery stores. It's quite easy to make at home, and is best that way.
1 quart half-and-half or light cream
1 packet crème fraîche culture
When purchasing dairy products for use in culturing or cheesemaking projects, it is very important not to buy ultra-pasteurized products because the extreme heat used during the process essentially kills the milk so that it will not respond well to culturing. Pasteurized or raw dairy will work fine, as will homogenized or creamline dairy. Raw and creamline tend to produce better results, but you may not be able to purchase raw milk where you live. The culture can be purchased at New England Cheesemaking Supply Company if you cannot find a local source.
How to Make Crème Fraîche at Home
If you prefer to make this without using a culture, there are instructions in my previous post about Crème Fraîche, as well as information about the basic home creamery setup you'll need.