Melt the butter and olive oil in a large flameproof casserole over medium heat. Add the chopped pancetta and cook, stirring, for 3-4 minutes until it starts to crisp. Add the onion, celery, carrot and garlic and cook, stirring, for 5 minutes or until softened. Add the beef and pork mince and cook for 8-10 minutes, breaking the meat up with a wooden spoon, until browned.
Add the milk and nutmeg and simmer over medium heat for 4-5 minutes until the milk evaporates. Add the tomato paste and stir for 2-3 minutes until combined, then add the wine and allow to simmer for 10 minutes. Add canned tomatoes, stock and herbs. Season with salt and pepper. Cover, then cook in the oven for 2 hours or until thickened and reduced. Skim any fat from the surface, then serve with pasta.
This will keep, sealed, in the fridge for 2-3 days, or frozen for 2 months.