1) Cook the pasta according to the directions on the packet.
2) Heat the oil over a medium heat in a large, deep saute pan. Saute the onion until soft and translucent, about 5 minutes. Add the garlic and cook an additional 1 minute.
3) Stir in the sausage and cook until heated through and browned, about 4 minutes. Add the escarole and cook until wilted, about 3 to 4 minutes.
4) Add the beans, 250ml of chicken stock, sage and red pepper flakes and simmer until the mixture is heated through and the liquid is slightly reduced.
5) Drain the pasta, add the sausage-bean mixture and toss well, loosening with the remaining chicken stock if necessary. Season with salt and freshly ground pepper to taste.
6) Divide the pasta dish between four pasta bowls and top with the grated Parmesan cheese.