Heat the butter and oil in a large pot over medium heat on the stovetop.
Add the diced celery, carrot, onion and pancetta and sauté until the vegetables have softened (approximately 5 minutes).
Turn the heat up to high and add the pork mince and beef mince. Stir occasionally (avoid stirring too much or you'll end up with a lot of liquid). Cook until the mince has browned and all of the liquid has evaporated. Note: To check if all of the liquid has evaporated, use a wooden spoon to make a gap in the base of the pot and see if there is any liquid there after a few seconds.
Add the rosemary sprigs and thyme.
Add the wine and cook until the liquid has evaporated.
Stir through the tomato paste.
Add the milk and stir through.
Pour in the chicken stock liquid, add the bay leaves and season with salt and pepper. Stir to combine.
Turn the heat down to low.
Cover with a lid and allow to cook slowly for a minimum of 1 hour (preferably 2-3 hours... the longer the better as the flavour develops beautifully as it cooks). Stir occasionally during the cooking time.
Remove the rosemary sprigs and bay leaves.
Cook pasta according to the packet instructions. Drain and return to the pasta pot. Add a large scoop of bolognese sauce and stir through.
Serve the pasta with extra bolognese sauce and grated parmesan cheese.