In a large Dutch oven, brown 1 pound of lean ground beef and 1 pound of ground sausage over medium heat for about 8–10 minutes, until well-cooked and browned. Drain excess fat, then add 1 diced carrot, 1 diced onion, 1 diced celery stalk, and 1 diced zucchini. Sauté the vegetables for 5 minutes until softened. Stir in 4 minced garlic cloves and your favorite seasonings, then pour in 24 ounces of marinara sauce. Let this simmer on low for 20 minutes, stirring occasionally.

In a separate saucepan, melt 4 tablespoons of butter over medium heat, then whisk in ¼ cup of flour to create a roux. Cook for 2 minutes until lightly golden. Gradually whisk in 2 cups of milk, allowing it to thicken for about 5 minutes until creamy. Remove from heat and stir in ½ cup of grated Parmesan cheese, mixing until smooth.

Bring a large pot of salted water to a boil and add your lasagna noodles, cooking them for about 8-10 minutes until al dente. If you're using no-boil noodles, skip this step. Drain the noodles and lay them flat on a clean kitchen towel or baking sheet.

In a greased 9x13-inch baking dish, start by spreading a layer of the Bolognese sauce on the bottom. Place a single layer of noodles over the sauce, followed by another layer of Bolognese, a layer of béchamel, and 1 cup of shredded mozzarella cheese. Repeat the layering process until all ingredients are used.

Preheat your oven to 375°F (190°C). Cover the assembled lasagna with aluminum foil and bake for 25 minutes. Remove the foil and continue baking for an additional 30 minutes until the top is bubbly and golden. Let it rest for 10 minutes before slicing.