What are the trinity in French cooking?
Mirepoix (cuisine)
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.[1] Mirepoix is the flavour base for a wide variety of Western dishes: stocks, soups, stews and sauces.