Along with death and taxes, chopping mirepoix is one of the few things a student of the culinary arts can be absolutely certain of. That's because mirepoix (pronounced "meer-pwah") is a fundamental element of classical cuisine; sort of the proton, neutron, and electron of the culinary arts.
So what is this mysterious mirepoix that keeps so many prep cooks so busy?
Three things: carrots, celery, and onions. When combined, these three simple ingredients, commonly referred to as "aromatics," come together to add flavor and aroma to stocks, sauces, soups, and other foods.
Cajun chefs use a variation on mirepoix which consists of three parts onions, two parts celery, and one part green bell pepper, and they take it so seriously they refer to it as "the holy trinity."
Traditional mirepoix consists of two parts onions, one part carrots, and one part celery, with the proportions determined by weight. Therefore, one pound (16 oz) of mirepoix would take 8 ounces of onions, 4 ounces of carrots, and 4 ounces of celery.
And if you're in culinary school, then, by all means, break out the scale. For that matter, do whatever your instructor tells you to do; not all chefs abide by this recipe precisely.
But if you're cooking at home, you can feel free to eyeball it. Mirepoix isn't something that needs to be calibrated to the exact gram. You could even use volume measurements (like two cups onions and one cup each of carrots and celery) instead of weight, and it'll still work fine.
When you're making stock, the mirepoix is ultimately strained out, so you don't need to be particularly precise when chopping the vegetables. The pieces should be more or less uniform in size, however, to allow for uniform cooking times.
The more finely mirepoix is chopped, the more quickly its flavor and aroma are released into a stock. Since the brown stock is simmered longer than white stock, it's perfectly acceptable to cut the mirepoix into pieces an inch or two in size. For white stock, a 1/2-inch dice is probably best.
- Leeks can be used in place of some or all of the onions.
- If you want a colorless stock, you can make a "white mirepoix" by substituting parsnips, mushroom trimmings, or both, for the carrots, or just omitting the carrots altogether.