Heat 2 tbsp of the olive oil in a large, deep pot on a medium heat. Add the shallots, garlic and lemon and cook down for about 10-12 minutes.
Add the beans and all of their liquid to the pan, then add the stock, Parmesan rind (if using) and salt and pepper. Bring to a boil and then turn down to a simmer and cook for 10-12 minutes.
Remove the Parmesan rind and the lemon, squeezing it against the side of the pot to release all of its juices. Stir in the cavolo nero and allow to wilt.
Divide between four bowls, drizzle with the remaining olive oil, gratings of Parmesan, the crispy shallots if using, and lots of black pepper.