Crème fraîche
Contrary to what the name might indicate, crème fraîche is made by culturing, or souring, cream. To make this decadent delight, heavy cream is pasteurized and bacterial cultures are then added to convert the natural sugars into lactic acid, yielding a thick, rich cream. Traditionally, crème fraîche is made using unpasteurized cream that is then cultured by the natural bacteria present in the environment. US standards require the milk and cream used to make cultured products be pasteurized first.
Crème fraîche is quite versatile and can be used in both savory and sweet dishes. With upwards of 30% butterfat (content is not standardized and can vary widely), it is richer, thicker, and less tangy than sour cream. It is particularly good added to sauces and soups because, due to its high fat content, it does not curdle in the heat. The slightly tangy, nutty taste also pairs well with fruit and is frequently used for desserts.