Cook lasagna noodles in a large quantity of boiling, salted water with 2 tablespoons oil. Cook 12-15 minutes, drain, spread on cooler to dry. Heat 1 tablespoon oil in a pan, fry onion, then add minced steak and brown. Add tomatoes, tomato paste, bay leaf, stock, salt and pepper. Bring to the boil and simmer 15 minutes. Melt butter in saucepan, add flour and cook 2 minutes. Add milk gradually, stirring all the time. Bring to the boil, cook 3 minutes. Stir through half Mozzarella cheese. Place meat sauce, cheese sauce and pasta in layers into a greased oblong ovenproof dish, finishing with sauce, sprinkle top with remaining grated cheese. Heat through in the centre of a gas oven 180°C for 30 minutes.