To make the sauce, stew the leeks, shallots and garlic in the butter in a heavy, covered pan. They will need about 20 minutes. Stir occasionally and add a little water if they start to stick. When the vegetables are quite soft, stir in the cream and Gorgonzola, and season with pepper and a little salt, if you wish.
Put the sauce to one side while you cook the pasta in a large pan