We choose to cook with small leeks, in particular a fast-growing variety called Pancho. This has long white stems when young, and its green tips are also very tender.
Try to buy leeks with their roots attached as this keeps them fresh. The leaves should be dark green and firm, the stalks white and stiff. Never use leeks that have begun to shoot as they will have lost their sweet taste and have tough centres.
Leeks always have sand or dirt stuck between their leaves. To clean, fill a sink with cold water and push the leeks up and down in it, leafy side down, to help release the dirt.
We use the white part of larger leeks instead of, or combined with, red onions in the base of fish risottos.