Step 1: Prepare the Meat Sauce

1. Heat a large skillet or saucepan over medium heat. Add the ground beef and Italian sausage, breaking them up with a wooden spoon. Cook until browned and fully cooked through. Drain excess fat if necessary.
2. Add the chopped onion to the pan and sauté for 3–4 minutes, or until softened. Stir in the minced garlic and cook for another minute until fragrant.
3. Pour in the crushed tomatoes, tomato sauce, and tomato paste. Mix well to combine.
4. Season with basil, oregano, red pepper flakes (if using), salt, and pepper. Stir to combine. Reduce the heat to low and let the sauce simmer for 30–40 minutes, stirring occasionally.

Step 2: Prepare the Ricotta Filling

1. In a large mixing bowl, combine the ricotta cheese, shredded mozzarella, grated Parmesan, egg, parsley, and a pinch of nutmeg. Stir until well blended. Set aside.

Step 3: Cook the Lasagna Noodles

1. Bring a large pot of salted water to a boil. Add the lasagna noodles and cook according to the package instructions until al dente.
2. Drain the noodles and lay them flat on a clean kitchen towel or parchment paper to prevent sticking.

Step 4: Assemble the Lasagna

1. Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking dish.
2. Spread a thin layer of meat sauce on the bottom of the dish. Place 3–4 lasagna noodles on top, slightly overlapping.
3. Spread a layer of the ricotta mixture over the noodles, followed by a generous layer of meat sauce.
4. Repeat the layering process until all the ingredients are used, finishing with a layer of meat sauce on top.
5. Sprinkle the remaining shredded mozzarella and grated Parmesan evenly over the top.

Step 5: Bake the Lasagna

1. Cover the baking dish with aluminum foil, ensuring the foil doesn’t touch the cheese. Bake in the preheated oven for 25 minutes.
2. Remove the foil and bake for an additional 20–25 minutes, or until the cheese is bubbly and golden brown.
3. Let the lasagna rest for 15 minutes before slicing and serving.