In a frying pan, sauté half a chopped onion in olive oil. Add the tomato puree, salt to taste and cook for about 10 minutes, stirring occasionally. In the meantime, as soon as the water for the pasta begins to boil, add salt and toss in the Fusilli. When the sauce is ready, turn off the heat and add the béchamel sauce, mixing well. Drain the pasta halfway through cooking and pour it into the pan with the sauce. Now add the diced mozzarella and the grated cheese, keeping some aside for gratin. Transfer the pasta to an ovenproof dish and place the rest of the mozzarella and grated cheese on top. Bake in a ventilated oven at 180° C for about 25 minutes or in a static oven at 190° C for the same time. Our irresistible tasty baked pasta is ready to be served at the table!