In a large skillet, heat a splash of olive oil and a tablespoon of butter over medium heat. Sauté diced pancetta until crispy, about 5 minutes. Add chopped onion, carrots, celery, and minced garlic, cooking until the vegetables are soft, roughly 8-10 minutes.

Incorporate the ground beef and Italian sausage into the mixture. Cook through, ensuring the meat is well-combined, about 6-8 minutes. Stir in tomato paste and let it cook for another 2-3 minutes.

Pour in the canned crushed tomatoes and red wine, scraping any browned bits from the bottom. Add milk, bay leaves, and the Parmesan rind, seasoning with salt and pepper. Simmer on low heat for 2.5 to 3 hours, stirring occasionally.

While the sauce simmers, bring a large pot of salted water to a boil. Add the lasagna noodles and cook until al dente, about 4 minutes. Drain and lay them flat on oiled parchment paper.

In a saucepan, melt 4 tablespoons of butter over medium heat, then whisk in flour. Stir for about 2 minutes until it forms a light roux. Gradually add warmed milk, whisking for 5-7 minutes until thickened. Stir in grated Parmesan, nutmeg, salt, and pepper.

In a greased 9x13 inch baking dish, spread a layer of béchamel sauce on the bottom. Begin layering with noodles, Bolognese, more béchamel, and optional mozzarella. Repeat this process until all ingredients are used, finishing with béchamel and additional Parmesan.

Preheat oven to 375°F and cover the assembly with foil. Bake for 1 hour, then remove foil and bake for an additional 15 minutes. Let the lasagna rest for 15 minutes before slicing.