Preheat the oven to 375°F (190°C).

In a large skillet, cook the ground beef and Italian sausage over medium heat until browned. Drain excess fat.

Add the diced onion and garlic to the skillet and sauté until the onion is translucent.

Stir in the crushed tomatoes, tomato paste, sugar, basil, salt, and pepper. Simmer for 30 minutes, stirring occasionally.

In a mixing bowl, combine the ricotta cheese, egg, 2 cups of mozzarella cheese, and half of the Parmesan cheese. Mix well.

Spread a thin layer of meat sauce at the bottom of a 9×13 inch baking dish. Layer 4 lasagna noodles on top.

Spread half of the ricotta mixture over the noodles, then add a third of the meat sauce and a sprinkle of mozzarella cheese.

Repeat the layering process: noodles, ricotta mixture, meat sauce, and mozzarella cheese until all ingredients are used, finishing with meat sauce on top.

Sprinkle the remaining mozzarella and Parmesan cheese over the top layer. Cover the dish tightly with foil.

Bake in the preheated oven for 25 minutes. Remove the foil and bake for an additional 25 minutes, or until the cheese is bubbly and golden.

Let the lasagna sit for 10-15 minutes before cutting and serving. Garnish with fresh parsley if desired.