Leek's are related to the onion family. They are sweet like onions when they are cooked, but unlike onions make your eyes water when you cut them, they have long straight white stalks with tough green leaves. Select white fresh stalks with bright looking green leaves, and avoid damage. To prepare the soup cut the stalk of the green leaf and reserve them to make stock and trim the surface of the base.Under running water cut the leek for two halves and wash thorughly between the layers. Slice them up with mixed vegetables as hotty winter soups.