In an 8 litre pot, saute pancetta in olive oil until soft. Add onion and celery; saute, stirring, for about 5 minutes. Stir in sage, 1 teaspoon salt and black pepper. Add chicken stock, cover and bring to the boil. Add beans and pasta, cover and simmer for 30 minutes.
Stir in minced parsley before serving, and sprinkle with grated Pecorino or Parmesan cheese if desired.