When Chefs use this term it sounds like an exotic ingredient or complicated culinary feat. It actuality, is a very basic combination of vegetables, diced & mixed together before sauteing. Some mirepoix combinations include leafy greens, as found in soup, and others contains meat, au gras, if you need the term.
Mirepoix is a French word/name, possibly stemming from the title of an 18th century French Diplomat named Charles Pierre Gaston Francois de Levis, Duke of Levis-Mirepoix. Mirepoix is a small town located in southern France.
Every cooking nationality has it’s mirepoix. A favorite blend of diced vegetables.
Italians call it soffritto; Portugese cooking: refogado; Poland: wloszczyzna and in Creole cooking: the holy trinity. Almost every nation has its typical combination & term.
My personal favorite combination is: onion, garlic, carrot, celery, rosemary & thyme.
It is an easy cooking base for any sauce, gravy, soup or stew. Next time you see the term, know its just veggies diced & sautéed!