Leeks are more than an onion stand-in, say Chowhounds. They’re terrific all on their own, particularly in preparations that showcase them. Try braising them whole in chicken stock or water and serving them with a mustardy vinaigrette and capers. Broiling is another good cooking method: Top leeks with melted butter and Gruyère or Parmesan before cooking. And you can slice them and sauté in butter to use in an omelet or frittata; or try making this potato and leek gratin with cumin (registration required).
Caralien makes a super-simple potato-leek soup that really lets the flavors of the leek and potato shine through. Combine leeks and a slightly greater volume of waxy potatoes, both thinly sliced, a generous amount of sea salt, and water. Simmer until the vegetables are tender, then purée. Others like to use chicken stock as the cooking liquid, and some finish the soup with cream. For a flavor twist, add garlic, nutmeg, cayenne, or dill seed.