Heat olive oil in a pot over medium heat.
Add onions and garlic and saute for several minutes, or until starting to soften.
Add Italian sausage and ground beef and cook until browned.
Drain off fat, leaving a bit behind for flavor and moisture.
Add tomatoes, tomato juice, salt, pepper, Italian seasoning, and red pepper flakes.
Stir and simmer for 25 to 30 minutes. After that time, remove 3 to 4 cups of the sauce to a different bowl to cool down.
Preheat oven to 375°F.
In a separate bowl, mix together the ricotta cheese, 2 cups of the grated mozzarella, Parmesan, egg, and salt and pepper. Stir together just a couple of times (do not mix completely).
Drain the pasta and rinse under cool water to stop the cooking and cool it down.
Pour it into the bowl with the cheese mixture and toss to slightly combine (there should still be large lumps.)
Add the cooled meat sauce and toss to combine.
Add half the coated pasta to a large casserole dish or lasagna dish.
Spoon half of the remaining sauce over the top, then top with half the remaining mozzarella cheese. Repeat with another layer of the coated pasta, the sauce, and the mozzarella. Bake for 20 minutes, or until bubbling. Remove from the oven and let stand 5 minutes before serving. Sprinkle chopped parsley over the pasta just before serving.
