Leeks, which are related to onions and garlic, look something like an oversized scallion. They have thick, white stalks with slightly bulbous root ends, and broad, flat, dark green leaves. The flavor of a leek is like onion but more herbaceous, though not like any herb in particular. But while onions add a single-edged sweetness, leeks add both sweetness and vegetable flavor. This is why they give depth and complexity and why, as a stand-alone vegetable, they’re especially interesting and flavorful.
Leeks are useful in so many dishes—in the same league as carrots, onions, and celery, and they make a great base for delicious stuffings, stews, soups, and sautés. But a leek’s unique combination of silky texture and herbal-sweet flavors can take center stage, too.
Leeks are available year-round, but they’re at their best from early fall through winter and into spring. When buying leeks, look for firm, undamaged stalks and fresh-looking, brightly colored tops—the darker the tops, the older and tougher the leeks. The edible parts of leeks are the white and light-green portions (the dark-green leafy tops are usually cut off and discarded or used to flavor broths), so ideally, you want leeks with as much white stalk as possible.
Cleaning: Since leeks are grown with soil piled all around them, there is plenty of opportunity for dirt and grit to settle between their onion-like layers. The easiest way to clean a leek is to trim the root end and the dark green tops and cut it in half lengthwise (or, if you want to retain the appearance of whole leeks in your dish, just cut about two-thirds of the way through the stalk). Hold the leek root-end-up under cold running water and riffle the layers as if they were a deck of cards. Do this on both sides a couple of times until all the dirt has been washed out.
Cooking: While garlic, scallions, and onions can be tossed into a dish raw, leeks must always be cooked, and when grilled, they first need a short parcooking. And while some vegetables benefit from al dente cooking, leeks definitely aren’t one of them. Which isn’t to say that they should be cooked to death, but in order to get tender, velvety leeks, you must cook them until they’re soft or you’ll get a fibrous, indigestible result.
Wrapped in a damp paper towel and stored in a plastic bag in the refrigerator, leeks will last at least a week.