Nigel Slater's spaghetti bolognese

Name: Nigel Slater's spaghetti bolognese
Prep time: 30 min
Cook time: 2 h
Total time: 2 h 30 min
Cuisine: Italian
Ingredients: 50g/1¾ oz butter; 70g/2½ oz pancetta; 1 onion, finely chopped; 2 cloves garlic, finely chopped; 1 carrot, finely chopped; 2 celery stalks, finely chopped; 2 large mushrooms, finely chopped; 2 bay leaves; 400g/14oz beef mince; 200ml/7fl oz whole milk; 220ml/7¾fl oz crushed tomatoes or passata; 200ml/7fl oz red wine; 200ml/7fl oz vegetable stock; pinch freshly ground nutmeg; spaghetti or tagliatelle, cooked according to packet instructions; grated parmesan cheese, to serve