The French word mirepoix describes a mixture of vegetables used to create an aromatic base of flavor for sauces, stews, stocks and many other dishes that go down especially well in these cold, dark days.

Classic mirepoix is typically two parts onion, one part carrot and one part celery, but it can be include other vegetables too, like leeks, fennel, thyme, parsley, parsnip or celeriac. And there are myriad variations, such as Cajun-style mirepoix--known colloquially as the Trinity--made from onion, celery and bell pepper, and Asian-style mirepoix made from ginger, garlic and scallion. What these variations have in common is that they provide an earthy foundation to whatever the ultimate dish may be.

One of the most common uses for mirepoix is stock, an important ingredient that should not be confused with soup, which is a finished dish. Many chefs don't even salt their stocks, preferring to save the seasoning until the final product is nearing completion. "If you're making risotto, salt in the stock can prevent the grains from absorbing water. You end up stirring and stirring until it's mush," says chef Jason Willenbrock, whose résumé includes a stint at Moulin de Mougin, a three-star Michelin restaurant in France.

Stock is usually made with mirepoix and bones, which add a gelatinous quality and a rich mouth-feel to the stock, thanks to their collagen content. Willenbrock is so into bones that he sometimes prefers them to the meat they carry. He starts by lightly rubbing turkey, chicken or beef bones with olive oil, and then oven-roasting them at 400 degrees for half an hour in a shallow baking dish, stirring occasionally.

 "You don't have to roast the bones," he says, "but it adds color and intensity of flavor."

He adds the roasted bones to a big soup pot full of water, along with a coarsely chopped mirepoix, either traditionally proportioned or whatever he has around--a variation he calls "kitchen sink mirepoix." Since it's going to cook for a very long time, the veggies needn't be chopped particularly finely, and can even be added whole.

Then Willenbrock adds chopped tomatoes--for an even richer color and an acidic bite--and aromatic spices like bay leaves, black pepper and thyme. He lets the stock cook slowly at barely a simmer for eight to 10 hours. Then he strains out the bones and veggies and freezes the stock.

You can also make vegetarian stock by oven-roasting your mirepoix with a little olive or sunflower oil until it's browned but not burned, and then following the same recipe without the bones. The stock won't have the collagen-rich mouth-feel or the meaty flavor, but it will still have those aromatic earth tones.

I have a chicken soup recipe I call "Cheater's Chicken Soup." Simply purchase a roasted chicken and put it in a pot with chopped mirepoix, salt and pepper and maybe some fresh dill or roasted green chiles. When the chicken softens enough, I pull the bones and skin out (saving the bones to make stock), and violà! So easy it must be cheating.

Another classic cold-weather use of mirepoix is in a braise. Braising is a technique best applied to tough cuts of meat, which usually have more flavor than the tender cuts. And they're cheaper. And they have more collagen. Braising belongs to the "low and slow" category of cooking, similar to what goes on in a crock pot, but much more tasty, in my opinion.

Most braising recipes call for browning the meat first in oil or fat, making sure that all sides are nicely browned but not burnt. But I follow the lead of the late, great James Beard, who preferred to brown his meat under a broiler, which is easier, produces a better brown and draws fat out rather than adding it.

 Place the browned meat on a bed of mirepoix in a baking dish, and add enough water (and/or stock, wine, sherry, etc.) to half-cover the contents. Cook slowly under a tight lid, which allows the steam to drip off the top and self-baste, and turn the meat occasionally to ensure even cooking. Add more liquid as necessary to prevent it from drying out and cook at 300 degrees until you can cut it with a spoon. It makes a dark and rich counterpoint to the dark, cold days of winter.

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