The French term for a mixture of finely chopped onions, carrots, and celery is mirepoix. It is a classic aromatic base used to build flavor in stocks, soups, sauces, stews, and braised dishes.
Traditional mirepoix commonly follows a 2:1:1 ratio: two parts onion to one part carrot and one part celery. The vegetables are usually diced and gently cooked in butter, oil, or another fat. Slow cooking softens them and brings out sweetness without necessarily browning them.
The word became associated with French cuisine in the 18th century and is linked to Charles-Pierre-Gaston de Lévis, Duke of Mirepoix. The technique itself is probably older than the name. In some preparations, cooks add meat, herbs, leeks, parsnips, or tomato paste.
Mirepoix is often confused with an Italian soffritto or the Cajun “holy trinity.” These are related flavor bases, but their ingredients and cooking traditions differ: the holy trinity replaces carrots with green bell pepper, while soffritto is typically cooked until more noticeably browned.