Heat the oil in a frying pan over a medium heat and fry the onion, celery and fennel for 5 mins. Add the garlic and pancetta, and fry for 5 mins more.

Stir in the beans, then add the tomatoes, tomato purée, stock and vinegar. Stir, bring to a simmer and cook, uncovered, for 10 mins. Season to taste.

For the gremolata, mix everything together in a small bowl. Set aside.

Spoon the ragu into bowls and top with the gremolata. Scatter over some parmesan, if using, and serve with crusty bread, if you like.