Leeks resemble a giant green onion, and are the mildest member of the onion family. Leeks are very popular in classic French cuisine, bringing a combination garlic/onion flavor - but very mild. Leeks are so mild that they can even be used raw in salads but are great additions to soups and casseroles as well. When selecting leeks, look for the smaller ones with dark green, crisp leaves that are blemish-free. The little roots should be light in color. Avoid dark and dry roots, and wilted or wrinkled leaves.