Step 1: Prepare Bolognese Sauce. In a large pot, cook the diced pancetta over medium heat until crispy, then remove it and set aside. In the same pot, use the rendered fat to sauté chopped yellow onion, carrots, celery, and minced garlic for about 5 minutes until softened. Add ground sirloin and Italian sausage, cooking until browned, then stir in tomato paste and simmer until fragrant.

Step 2: Simmer Sauce. Pour in the medium-bodied red wine, scraping the bottom of the pot to release any flavorful bits. Then add the canned crushed tomatoes, bay leaves, and Parmesan rind to the pot. Season with salt and pepper, and let the sauce simmer on low heat for 2.5 to 3 hours, stirring occasionally until rich and thick.

Step 3: Cook Lasagna Noodles. As the sauce simmers, bring a large pot of salted water to a boil. Cook the lasagna noodles according to package instructions, about 4 minutes until al dente. Drain the noodles and lay them flat on a baking sheet brushed with olive oil to prevent sticking while you prepare the béchamel sauce.

Step 4: Make Béchamel Sauce. In a saucepan, melt 5 tablespoons of unsalted butter over medium heat. Whisk in 1/4 cup of all-purpose flour, stirring constantly for about 2 minutes until light golden. Gradually add 4 cups of warmed whole milk, continuing to whisk until the sauce thickens and bubbles, approximately 10 minutes. Stir in half of the grated Parmesan, nutmeg, salt, and pepper for extra flavor.

Step 5: Assemble Lasagna. Preheat your oven to 375°F (190°C). In a greased 9x13 inch baking dish, spread a thin layer of béchamel sauce on the bottom, followed by a layer of noodles. Alternate layers of Bolognese, béchamel, diced mozzarella, and more grated Parmesan, repeating until all ingredients are used. Finish with a final layer of béchamel topped with mozzarella and the remaining Parmesan.

Step 6: Bake the Lasagna. Cover the assembled lasagna with foil and bake it in the preheated oven for 1 hour. After that, remove the foil and continue baking for an additional 15 minutes, allowing the top to become golden and bubbly. Once baked, let the Classic Lasagna Bolognese rest for 20-30 minutes before slicing.