Prepare the Meat Sauce:

1. In a large saucepan, heat olive oil over medium heat. Add pancetta and cook until slightly crisp.
2. Add finely chopped onion, carrot, and celery. Sauté until softened.
3. Stir in minced garlic and cook until fragrant.
4. Add ground beef or pork, breaking it apart with a spoon, and brown evenly.
5. Pour in red wine and let it reduce for a few minutes.
6. Stir in tomato paste and canned tomatoes, breaking the tomatoes up with a spoon.
7. Season with salt, black pepper, and a bay leaf. Simmer for at least an hour, stirring occasionally.

Prepare the Béchamel Sauce:

1. In a separate saucepan, melt butter over medium heat.
2. Whisk in flour and cook for a minute until golden.
3. Gradually add warm milk, whisking continuously until smooth.
4. Season with salt, black pepper, and a pinch of nutmeg. Continue stirring until thickened.

Assemble the Lasagna:

1. Preheat the oven to 375°F (190°C).
2. In a baking dish, spread a thin layer of meat sauce.
3. Add a layer of lasagna sheets, followed by more meat sauce, béchamel, and grated Parmesan.
4. Repeat layers until all ingredients are used, finishing with béchamel and mozzarella on top.

Bake the Lasagna:

1. Cover with foil and bake for 30 minutes.
2. Remove the foil and bake for another 15 minutes until golden and bubbling.
3. Let it rest for 10 minutes before slicing and serving.