In a Dutch oven, cook pancetta over medium heat until crispy, about 5-7 minutes; remove and set aside. Finely chop onion, carrot, and celery in a food processor, then add them to the pot, cooking until softened, roughly 8-10 minutes. Stir in ground beef and pork, cooking until browned. Add tomato paste, red wine, and crushed tomatoes, followed by bay leaves, salt, and pepper. Let the Bolognese sauce simmer on low heat for 2.5 to 3 hours until thick and flavorful.

Bring a large pot of salted water to a rolling boil and gently add the egg lasagna noodles. Cook for about 4 minutes, or until al dente; they should remain firm as they will continue cooking in the oven. Drain the noodles and drizzle with olive oil to prevent sticking. Set aside to cool.

In a saucepan, melt 5 tablespoons of unsalted butter over medium heat. Whisk in ¼ cup of all-purpose flour, stirring constantly for about 2-3 minutes until golden and bubbling. Gradually add 4 cups of warmed milk while continuing to whisk until the mixture thickens, around 5-7 minutes. Stir in ⅛ teaspoon of freshly grated nutmeg and 1 ¼ cups of freshly grated Parmesan, mixing until smooth. Remove from heat and set aside.

Preheat your oven to 375°F (190°C). Grease a 9"x13" baking dish and begin layering by spreading a thin layer of béchamel sauce on the bottom. Place a single layer of lasagna noodles, followed by spoonfuls of Bolognese and another layer of béchamel. Scatter diced fresh mozzarella and add more Parmesan. Repeat the layers until all ingredients are used, finishing with béchamel sauce and the remaining cheeses on top.

Cover the assembled Lasagna Bolognese with aluminum foil and bake in the preheated oven for 1 hour. After the hour, remove the foil to allow the top to become golden and bubbly, baking for an additional 15 minutes. Let the lasagna rest for 20-30 minutes to set before slicing and serving.