The edible part of a leek is the white part plus an inch or so of pale green. Smaller leeks are more tender, making them perfect for grilling or braising, while larger leeks are perfect for soup and gratins. Due to how leeks are grown, they often have lots of dirt between the leaves so they need to be washed well. Cut off the greens an inch above the white part and slice off the roots, leaving a thin piece attached so that the leaves remained joined at the base. Halve the leeks lengthwise down the middle to the root end. Rinse well under running water while you fan the leaves to make sure you are getting dirt stuck between leaves. Cut leaves can also be rinsed after cutting. If using in a soup, leeks do not caramelize well so they are best lightly cooked. In addition to the classic Vichyssoise and Cock-a-Leekie soups, leeks go well with potatoes, fennel, celery, capers, parmesan, goat cheese and olives.