Leeks have a small root and thick, sheath-like stem, made up of flat encircling leaves, which flatten as they taper upwards.
When buying, look for a bright fresh colour and firm dark leaves - and steer clear of any with yellowing or drooping leaves.
To prepare, slice off the root and remove the outer leaves, then rinse out any trapped soil between remaining leaves.
Ideal for cream and broth-style soups, they make an ideal companion to potatoes. Classic dishes include vichyssoise - a creamy celery, leek and potato soup.