Leeks look like jumbo-sized green onions but have their own sweet, mild flavor. A favorite in French cooking, they are grown in mounds of dirt, which keep the white part of their stem from seeing the sun. This process is called blanching. One side effect is that leeks can be very gritty and need to be thoroughly cleaned before cooking. All portions of the leek are edible, but they are utilized in different ways.
The white shaft that begins at the root end of the leek is the portion that is most frequently called for in recipes. Most commonly, it is thinly sliced or diced and then sauteed. Leek whites can be eaten raw but tends to be on the chewy side; heat helps soften them and release their flavor.
Light Green Shaft
The light green portion of the leek is usually utilized alongside the white portion, although some dishes ask you to discard it. It's a little tougher than the whites but otherwise similar in flavor.
Dark Green Leaves
The dark green leaves of the leek both have less flavor than the stem and are significantly tougher, and so this portion is often discarded. However, the leaves can be saved to add flavor to vegetable or chicken stock. One or two of the leaves can also be tied into a bundle of herbs as part of a bouquet garni, used to flavor stews and other long-simmered French dishes.
Small, slim leeks are sometimes steamed, braised or grilled and served whole. You will still want to trim off the very top tips of the leaves, which tends to get bruised and ragged during transport and storage.
The history of leeks as a vegetable goes back all the way to ancient Egypt. The Roman Emperor Nero used to eat leek soup every day to keep his voice supple and sonorous for speech-making. Leeks are also the national symbol of Wales.