Lasagne alla Bolognese

Name: Lasagne alla Bolognese
Ingredients: For the ragu:; 1 pound (500 gr) total of mince beef and pork; 2 slices of rigatino or pancetta, chopped; 1/2 carrot, finely chopped; 1/2 celery stalk, finely chopped; 1 small onion, finely chopped; a handful of parsley, leaves and stalks finely chopped; 2-3 pinches salt; white wine to cover (about half a bottle); 8 ounces (250 ml) of tomato puree; For the bechamel and assembly:; 3 1/2 tablespoons (50 gr) butter; 1/2 cup (50 gr) flour; 2 cups (500 ml) cold milk; 3 1/2 ounces finely grated Parmesan cheese; 1 pound (500 gr) pasta sheets (fresh, dried or homemade)