Sort through beans to pick out bad ones and foreign matter, and soak beans in water three hours to overnight.
In a large saucepan or Dutch oven, cook onions and pancetta in olive oil over medium heat until onions become brown slightly. Add carrots, leeks, garlic and crushed red pepper and saute until tender.
Let soup simmer slowly for at least two hours, stirring every now and then. Add the rest of the chicken stock and three cups of water as needed to keep the soup liquid. Skim excess fat from the soup, but don't be too thorough about this--a little fat adds richness. The aroma should be wonderful.
When the beans in the soup begin to get tender, cook the pasta, drain it, and add it to soup. Stir well and serve with grated Parmesan cheese sprinkled over the soup at the table.