Blitz the onion, celery and carrot into a puree.
Heat olive oil in a large saucepan and gently fry the pureed veg for around 5 minutes before adding the garlic cloves and cook until fragrant.
Crumble in the pork mince and use a whisk to help break it up in the pan. Salt generously.
Once the pork starts releasing its juices, add the red wine and let it reduce, before throwing in the tomato paste, whole tomatoes and stock.
Squeeze the sausage meat out of its casing into a bowl and use the same whisk trick to break the meat up, before crumbling it into the sauce.
Add the bay leaves and Parmigiano rind, if using, and a cup of milk.
Allow this all to bubble away on the lowest possible heat for 3-4 hours, stirring occasionally - add a touch more stock if needed but you want this to reduce.
Discard the bay and Parmigiano rind before serving.