Crème Fraîche

Cream inoculated with lactic acid bacteria, triggering a fermentation that thickens it and develops a brown butter and hazelnut aroma (linked to the production of diacetyl), as well as a delicious tangy acidity. Although it melts admirably on hot meat or in mashed potatoes, its fermentation alters its thermal stability: direct boiling often causes it to "split." It is generally incorporated off the heat, or as a finish to provide a powerful acidic counterpoint to rich sauces.