Preheat your oven to 350°F (175°C).
Boil salted water and cook the lasagna noodles until they are al dente, about 8-10 minutes. Drain them and rinse with cold water.
Brown the beef and sausage in a skillet over medium heat with onion and garlic until no longer pink, about 5-7 minutes. Drain excess fat.
Stir in the pasta sauce, tomato paste, Italian seasoning, salt, and pepper. Let it simmer for 5 minutes.
Mix the cheese filling with mozzarella, Parmesan, ricotta, parsley, beaten egg, and a pinch of salt in a medium bowl.
Assemble the lasagna in a 9×13-inch baking dish: Start with meat sauce, layer noodles, cheese mixture, and repeat for a total of three layers.
Bake covered with foil for 45 minutes, then uncover, add remaining mozzarella and Parmesan, and bake for an additional 15 minutes.
Rest for at least 15 minutes before slicing and serving.