1Prepare the vegetables by chopping the onion, peeling and chopping the carrots, chopping the celery, and mincing the garlic.
2In a large pot, sauté the vegetables in olive oil.
3Add the sweet sausage and the ground meat mixture (beef, pork and veal) to the pot and cook until browned.
4Add the tomato paste and cook for a few minutes, then deglaze with white wine.
5Add the crushed tomatoes and simmer until the sauce has thickened.
6Make the pasta dough by combining flour, eggs, salt, and olive oil.
7Knead the dough until smooth and elastic, then let it rest, covered.
8Make the béchamel sauce by melting butter in a saucepan, whisking in flour, and gradually adding milk until smooth and creamy. Season with nutmeg, salt, and pepper.
9Roll out the pasta dough thinly using a pasta machine.
10Blanch the pasta sheets for 10 seconds in boiling water, then immediately transfer to an ice bath to cool and stop the cooking process.
11Assemble the lasagna by layering the sauce, pasta sheets, ricotta cheese, and mozzarella cheese in a baking pan.
12Top with the remaining sauce and mozzarella cheese, then bake until golden brown and bubbly.