Preheat oven to 375° F. Heat oil in a large pan over medium heat. Add onions and garlic and sauté until softened, several minutes.
Add sausage and ground beef, cook until browned. Drain off excess fat.
Add crushed tomatoes, diced tomatoes, basil, Italian seasoning and red pepper flakes; stir to combine. Reduce heat to simmer and cook for 25 to 30 minutes. After the cook time remove 3 to 4 cups of the sauce to a bowl to cool down.
In a separate bowl combine ricotta cheese, 1½ cups mozzarella cheese, Parmesan cheese, egg, salt, and black pepper. Stir together but do not mix completely. Add the pasta and toss slightly to combine. Add cooled meat sauce and toss to combine.
Add half of the coated pasta to a 9x13 inch baking dish. Spoon half of the remaining sauce over the top, and then top with half the remaining mozzarella cheese. Repeat with another layer of coated pasta, sauce and cheese.
Bake for 20 minutes or until bubbling. Remove from oven and allow to cool for 5 minutes before serving. Sprinkle parsley over pasta before serving.