The ultimate lasagne

Name: The ultimate lasagne
Prep time: 1 h
Cook time: 2 h
Total time: 3 h
Cuisine: Italian
Ingredients: 4 tbsp olive oil; 4 celery sticks, finely chopped; 2 carrots, finely chopped; 1 medium onion, finely chopped; 2 garlic cloves, peeled and crushed; 1 sprig rosemary; 700g/1lb 9oz beef mince; 340g/12oz pork mince; 1 bottle red wine (750ml/26½fl oz); 2 x 400g/14oz cans tomatoes, roughly chopped; 200ml/7fl oz beef stock; salt and freshly ground black pepper; 1 litre/1¾ pints whole milk; 2 bay leaves; ¼ onion; pinch freshly grated nutmeg; 50g/2oz butter; 50g/2oz plain flour; 14 sheets fresh lasagne pasta; 3 125g/4½oz balls mozzarella, cut into small cubes; small handful grated parmesan; freshly ground black pepper; 2 tbsp butter