A mirepoix (pronounced meer-pwah) is a French term consisting of a combination of chopped carrots, celery and onions used to add flavor and aroma to stocks, sauces, soups and other foods. These are considered your base aromatics.
Add to this mixture one of my favorite herbs thyme, and you are good to go for any soup, stock or sauce base. A similar trio, the Holy Trinity of Cajun cooking is made up of onion, celery, and bell pepper, but for all else, this is the master.
Some people claim that without one “what would it matter?” but it would change the finished product. Just because one flavor doesn’t stand out doesn’t make it’s presence needed, it is the combination of the three that completes the flavor and aroma value. These provide the basis, the body, the essence of your stock in partnership with the chicken, beef or veal bones and water. Side by side with herbs this enlightens the palette and makes for a more full flavored soup or stock base for any recipe.