Heat the oven to 190C/170C fan/gas 5. Put the mince in a shallow roasting tin, break it up and put in the oven for 5 mins. Remove the mince and give it a stir, then nestle in the star anise and cloves (tie them up in a piece of muslin cloth first, if you prefer) and roast for another 10 mins. Give it another stir, then roast for another 30-40 mins until deep brown and crispy, stirring and scraping it off the bottom of the pan a few times if needed. Set aside.
Meanwhile, heat the oil in a large saucepan over a medium heat and cook the pancetta for 8-10 mins until crispy and browned on all sides. Stir in the onions, carrots, celery and garlic, and cook for 8-10 mins until the veg has softened. Stir through the mushrooms, oregano and bay leaves, then scatter over the sugar and squeeze in the tomato purée. Stir well, then pour in the wine and vinegar and bring to the boil. Simmer for a few minutes until reduced by about a third.
Tip in the tomatoes, then a can of water. Add the stock pot or cube, give everything another good stir and bring to a simmer again. Scrape in the roasted mince and spice bag, season, then turn the heat down to low and simmer gently for about 1 hr 30 mins until thick and glossy. Taste for seasoning. The sauce will taste even better if left to cool completely and chilled for a day or two before reheating. Serve with pasta and grated parmesan, if you like. Can be chilled for up to three days or frozen for three months – defrost fully before reheating over low to medium heat until piping hot.