Preheat your oven to 375°F (190°C).

In a large pot, heat the olive oil over medium heat. Add the ground beef, Italian sausage, and diced onion. Cook until the meat is browned and the onion is softened, about 5-7 minutes.

Stir in the minced garlic and cook for another minute until fragrant.

Add the crushed tomatoes, tomato paste, dried basil, dried oregano, salt, and pepper. Let this simmer on low heat for about 20 minutes, stirring occasionally.

While the sauce is simmering, cook the lasagna noodles according to the package instructions. Drain and set aside.

In a mixing bowl, combine the ricotta cheese, egg, and a pinch of salt and pepper. Mix well until creamy.

To assemble, spread a thin layer of the meat sauce on the bottom of a 9x13 inch baking dish. Layer 4 lasagna noodles over the sauce.

Spread half of the ricotta mixture over the noodles, followed by a layer of meat sauce and a third of the mozzarella cheese. Repeat the layers: noodles, ricotta, meat sauce, and mozzarella.

Top with the remaining noodles, meat sauce, and sprinkle the remaining mozzarella and Parmesan cheese on top.

Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes. Remove the foil and bake for another 15-20 minutes, or until the cheese is bubbly and golden.

Once done, let the lasagna rest for about 10 minutes before slicing and serving.