Bolognaise rotolo

Name: Bolognaise rotolo
Ingredients: 450g pork and veal mince; 2 celery sticks, finely chopped; 1 large carrot, peeled, finely chopped; 1 large zucchini, finely chopped; 1 small brown onion, finely chopped; 2 garlic cloves, crushed; 700g btl passata (tomato pasta sauce); 375ml (1 1/2 cups) Massel chicken style liquid stock; 5 fresh lasagne sheets; 125ml (1/2 cup) tomato puree; 50g (1/2 cup) coarsely grated mozzarella; 2 tablespoons shredded parmesan; 2 tablespoons pine nuts; 15g butter; 1 1/2 tablespoons plain flour; 250ml (1 cup) milk