Slowly cook sliced leeks in olive oil and butter until soft, then toss with beans and pasta. Cook with potatoes and vegetable broth, the puree for a classic potato-leek soup. Slow-cook with butter and cream and serve with seafood such as seared scallops. Grill whole or halved leeks and serve as a starter or topping for bruschette. Add sauteed leeks to quiche, savory tarts or pies.