Mirepoix is a mix of diced onion, carrot and celery, cooked slowly in fat at the start of a soup, stew or stock to give it a sweet, savory base. The classic proportion is two parts onion to one part carrot and one part celery, measured by weight. You cut the three to a size that suits the dish, then cook them gently in butter or oil until soft, without letting them brown.

If you have ever started a pot of chicken noodle soup by softening onion, carrot and celery, you have made mirepoix. The French name only describes what many American kitchens already do.

Where the name comes from

The word is French and dates from the 18th century. It is named after Charles-Pierre-Gaston François de Lévis, duc de Lévis-Mirepoix, a French field marshal and ambassador, whose cook is credited with establishing the technique. The term did not appear regularly in French culinary texts until the 19th century.

The idea itself is older and wider than the name. Cooks across Europe and the Americas start their pots with a small set of aromatic vegetables, and the set changes with the cuisine:

  • Soffritto, in Italy: onion, carrot and celery cooked slowly in butter or olive oil, sometimes with garlic, shallot or leek.
  • Sofrito, in Spain and Portugal: onion, garlic and tomato.
  • Suppengrün, in Germany: leeks, carrots and celeriac, often with herbs.
  • The holy trinity, in Cajun and Creole cooking: onion, celery and bell pepper.

The trinity is the American cousin most cooks know by name. The holy trinity for gumbo covers how it is cut and cooked.

The 2:1:1 ratio

Onion makes up half the mix and softens into a sweet, mellow base. Carrot adds color and its own sweetness. Celery adds a green, savory note that keeps the mix from tasting flat.

The ratio is by weight, which matters because a cup of diced celery and a cup of diced onion do not weigh the same. If you have a kitchen scale, weigh it. If you do not, start with one large onion, two medium carrots and two ribs of celery for a typical pot of soup, and adjust by eye: the onion pile should look about as large as the other two together.

For a white stock, cooks swap the carrots for parsnips so the color stays pale. The same swap works for a light cream soup.

How to cut it

The size of the cut follows the cooking time. Mirepoix for a long simmer can be cut larger, and mirepoix for a quick soup should be cut small, so the vegetables finish softening when the rest of the pot is done.

Onion. Halve the onion through the root, peel it, and lay each half flat. Make vertical cuts toward the root without cutting through it, then slice across to dice. The root holds the layers together while you work.

Carrot. Peel and trim. Cut into lengths of about 3 inches, slice each length into planks, the planks into sticks, and the sticks across into dice. How to cut carrots goes into each step.

Celery. Wash the ribs and trim the ends. If the outer ribs are stringy, run a vegetable peeler down the curved back. Split wide ribs lengthwise into two or three strips, then cut across into dice.

Which size for which pot

  • Stock (several hours): large chunks, 1 to 2 inches, or the vegetables halved. They will be strained out. Chicken stock from scraps uses exactly this kind of rough cut.
  • Stew and pot roast (1 to 3 hours): a large dice, about ¾ inch, so the pieces hold their shape.
  • Chicken noodle soup, split pea, lentil (under an hour): a medium dice, about ½ inch, so every spoonful gets a little of each.
  • Sauces and fine soups: a small dice, about ¼ inch, which melts into the base.

Whatever size you choose, keep the three vegetables at the same size as each other. Carrot is the firmest of the three, so if anything, cut it a little smaller. Small, medium and large dice has the measurements side by side.

How to cook it

Classic mirepoix is cooked in fat, usually butter, over low heat for a long time, without coloring or browning. The goal is to soften the vegetables and draw out their sweetness rather than caramelize them.

  1. Melt butter or warm oil in the soup pot over medium-low heat.
  2. Add the onion first, with a pinch of salt, and stir until it begins to soften.
  3. Add the carrot and celery and keep cooking, stirring now and then, until everything is soft and the onion is translucent.
  4. If the edges start to brown, lower the heat and add a splash of water or stock.

Then add the rest of the soup: stock, meat, beans, tomatoes or herbs. Browning has its place in a darker stew or a gravy base, where a little color on the vegetables deepens the flavor. For a clear chicken soup, keep it pale.

Cut it ahead

Mirepoix is one of the most useful things to prep in advance. Cut a double batch on the weekend and keep it in a covered container in the refrigerator, at 40°F or below, and the next pot of soup starts in the time it takes to melt the butter.

Cut the three vegetables on one board and scrape them into the pot in order, onion first. The WONAMU. bamboo cutting board is 12 by 9 inches, enough room to keep onion, carrot and celery in three separate piles while you work. Wash it with warm soapy water afterward and dry it standing on edge.

The short version

Mirepoix is onion, carrot and celery, two parts onion to one part each of carrot and celery by weight. Cut all three to the same size, large for long simmering and small for quick soups.

Cook them gently in butter or oil until soft and translucent, without browning, then build the soup on top. For a pale stock, use parsnip in place of carrot.

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WONAMU. makes a bamboo cutting board designed for daily prep, 12 × 9 inches, bamboo, with a perimeter juice groove. Available on Amazon.

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