Heat 1½ tbsp oil in a large skillet over a low to medium heat. Add the onion, celery and carrots with a pinch of salt. Cook for around 10 minutes, stirring occasionally, until softened. Transfer to a plate.
Pour the remaining oil into the pan, increase the heat and tip in the ground pork and beef. Cook until golden. Break down the grounds with the back of a spoon as it cooks.
Return the vegetables to the pan and add the bay leaf and tomato paste. Cook for a 1 minute more and mix well. Pour in the wine and reduce by half. Add the stock and tomato sauce or juice with some salt (as needed) and bring to a boil. Reduce the heat to medium and let the sauce cook for 35-40 minutes, stirring occasionally, until reduced by half and you are left with a thick sauce.
Bring a large saucepan of salted water to boil 15 minutes before the sauce is ready. Drop in the pasta, cook following pack instructions until al dente, then drain.
Stir in the milk and season to taste. To serve, put pasta onto a plate and top with the Bolognese. Serve with grated parmesan.