1. Preheat your oven to 375°F (190°C).
2. In a large skillet over medium heat, cook the ground beef and Italian sausage until browned. Drain excess fat.
3. Add the diced onion and minced garlic to the skillet, sautéing until the onion is translucent.
4. Stir in the crushed tomatoes, tomato paste, oregano, basil, salt, and pepper. Let simmer for about 20 minutes, stirring occasionally.
5. While the sauce simmers, cook the lasagna noodles according to package instructions. Drain and set aside.
6. In a bowl, combine the ricotta cheese, egg, and half of the chopped parsley.
7. To assemble the lasagna, spread a thin layer of meat sauce on the bottom of a 9×13 inch baking dish.
8. Place three lasagna noodles on top of the sauce. Spread half of the ricotta mixture over the noodles, followed by a third of the mozzarella cheese and a sprinkle of Parmesan.
9. Repeat the layers, ending with noodles topped by the remaining meat sauce and cheeses.
10. Cover with foil and bake for 25 minutes. Remove the foil and bake an additional 15 minutes, or until the cheese is bubbly and golden.
11. Let the lasagna cool for 10 minutes before slicing. Garnish with the remaining parsley before serving.

Remember, patience is key. Letting the lasagna rest before serving allows the layers to set beautifully, making each slice a picture-perfect piece of culinary art.