Remove the outer leaves from the leeks, and then chop off the stems and leafy green tops. Cut the leeks into thin rings. Rinse thoroughly. Heat the olive oil in a large skillet over medium heat, add the pancetta and cook until golden. Add the leeks and sauté them until they begin to turn golden. Add about a cup of water, and salt and pepper, and the cook for about 10 minutes, until they are soft and most of the liquid is absorbed.
Bring a large pot of water to a boil. Cook the pasta until al dente, and then drain, retaining 1 cup of the cooking water. Add the pasta to the skillet with the leeks and cook together for about a minute, adding some of the retained water if it seems dry.
Serve immediately with a sprinkle of Parmigiano-Reggiano.