Heat the oil in a large flameproof casserole dish over a medium-high heat. Once shimmering, add the sausages and quickly stir to coat in the oil. Cook for 5-7 mins until browned all over, then scoop out and set aside on a plate. Turn the heat down to medium and stir in the onion, celery and carrot with a big pinch of salt. Cook for 8-10 mins until softened but not coloured.

Stir in the garlic, paprika and fennel seeds, if using, and cook for another 1-2 mins until fragrant. Stir in the herb sprigs and the tomato purée. Stir well to coat everything and cook for 5 mins until the tomato purée has caramelised and turned dark red. Add the vinegar, tomatoes, stock and beans, along with their liquid, then rinse out the tomato can with water and add that too. Bring to a simmer and return the sausages to the pan. Simmer gently for 40-45 mins, stirring frequently, until the sauce has thickened. Season to taste, remove the herb sprigs and discard.

Drizzle over the pesto and serve with warm crusty bread, if you like.