A mirepoix (/mɪərˈpwɑː/ meer-PWAH, French: [miʁ.pwa]) is a mixture of diced vegetables cooked with fat (usually butter) for a long time on low heat without coloring or browning. The ingredients are not sautéed or otherwise hard-cooked, because the intention is to sweeten rather than caramelize them. Mirepoix is a long-standing part of French cuisine and is the flavor base for a wide variety of dishes, including stocks, soups, stews, and sauces.
When the mirepoix is not precooked, the constituent vegetables may be cut to a larger size, depending on the overall cooking time for the dish. Usually the vegetable mixture is onions, carrots, and celery (either common 'Pascal' celery or celeriac), with the traditional ratio being 2:1:1—two parts onion, one part carrot, and one part celery. Further cooking, with the addition of tomato purée, creates a darkened brown mixture called pinçage. (Full article...)