A culinary preparation created in the 18th century by the cook of the Duc de Levis-Mirepoix, a French field marshal and ambassador of Louis XV. It consists of a mixture of diced vegetables (carrot, onion, celery); raw ham or lean bacon is added when the preparation is au gras (with meat).
A mirepoix is used to enhance the flavors of meat, game and fish, in the preparation of sauces, and as a garnish for dishes.
When a mirepoix is used in braised or pot-roasted dishes, it should be simmered gently in a covered pan until all the vegetables are very tender and can impart their flavor to the dish.
Source: Larousse Gastronomique