Like onions, to which they are related, leeks are most frequently used to add flavour to various dishes, particularly stews and soups (the best known is vichyssoise, the classic cold potato and leek soup from France). Leeks have a milder and sweeter flavour than onions and a crunchy texture when cooked, making them a delicious side dish served on their own. Leeks are surprisingly nutritious, supplying more vitamins and minerals than an equal sized serving of onions or spring onions (scallions).

Buying
Leeks resemble overgrown scallions, but are usually displayed in bunches of three or four but sometimes they are sold separately. Unfortunately, many markets sell bunches of leeks of wildly different sizes, making it difficult if you plan to cook the leeks whole.

While the white ends of scallions may be bulbous, those of leeks should be relatively straight and not exceed 1 1/2" in diameter, larger leeks may be a little stringy, and far less tasty. Check each leek at both ends: The leaf tops should be fresh and green, while the white root end should show a firmly attached fringe of rootlets and several inches of unblemished skin, which will give very slightly to pressure. Avoid leeks with obvious signs of age or mishandling, such as wilted or torn greens or split or oversized bulbs.

Some markets also carry baby leeks, which can be pencil thin and are more tender than medium-sized leeks, try wrapping these in parma ham, drizzle with a cheese sauce and grill for a few minutes.

Storage
Leeks will keep for up to a week in the refrigerator. Store them loosely wrapped in plastic, this not only helps them retain moisture, but also prevents their odour from spreading to other foods. Trim the leeks only when ready to prepare them.

Preparation
Cooked and served whole, leeks make an excellent side dish or appetiser. They can also be chopped or sliced for use as an ingredient in other dishes.

Leeks often require careful cleaning as soil and grit collects between the layers of the broad overlapping leaves. Remove any withered or toughened outer leaves. Trim off the darkest portion of the green tops (the whole leek is edible, but the darker green portions have a stronger, less pleasant flavour). Trim the rootlets at the base.

If cooking leeks whole, insert a knife about 1" below where the leaves start to turn green and slice lengthwise to the top end. Then roll the leek a quarter turn and make a second lengthwise slit perpendicular to the first. Fan the leaves apart and wash under cool running water. Dirt collects on a leek where it rose above the soil and starts to turn green.

Cut leeks as directed in the recipe and place the leeks in a bowl of lukewarm water. Swish the leeks around in the water and scoop them out. The dirt will settle to the bottom of the bowl.

Leeks can quickly overcook, which turns them soft and slimy. Also, they continue to cook after they are removed from heat (unless you plunge them into cold water). If serving them hot, cook until just barely tender, you should be able to slightly pierce the base with the point of a sharp knife. Since cooking times vary, depending upon the size and age of the leeks, you will need to keep testing to see if they are cooked..