Heat the oil in a large saucepan or flameproof casserole over a medium heat and fry the onion, celery and carrot with a pinch of salt for 15 mins until soft. Add the garlic and chilli flakes, and cook for 1 min.

Stir in the rosemary sprig, tomatoes, stock, beans and parmesan rind, if using, and bring to a simmer. Add the cavolo nero and cook, covered, for 10 mins. Stir through the bread and cook for several minutes more to warm through, then add the vinegar and season. Spoon into bowls, drizzle with a little more oil and sprinkle with the basil, if using, and the grated cheese.