Step 1: Heat the olive oil in a large Dutch oven or heavy-bottomed pot over medium heat.
Step 2: Add the ground beef and Italian sausage. Break up the meat with a spoon and cook until browned, about 8-10 minutes. Drain any excess fat.
Step 3: Add the diced onion, minced garlic, and Italian seasoning to the pot. Cook until the onion is softened and translucent, about 5-7 minutes, stirring occasionally.
Step 4: Stir in the crushed San Marzano tomatoes, tomato paste, beef broth, and red pepper flakes (if using). Bring the mixture to a simmer.
Step 5: Reduce the heat to low, cover, and let it cook for at least 15-20 minutes, allowing the flavors to meld. Stir occasionally.
Step 6: While the sauce simmers, prepare the cheesy topping. In a medium bowl, combine the whole milk ricotta cheese, 1/2 cup of shredded mozzarella, 1/4 cup of grated Parmesan cheese, fresh parsley, salt, and black pepper. Stir until well combined. Set aside.
Step 7: Uncover the soup, and increase the heat to medium-high. Add the broken lasagna noodles directly to the simmering soup. Stir well to ensure the noodles are submerged.
Step 8: Cook the noodles according to package directions (usually 8-10 minutes), or until al dente. Stir occasionally to prevent sticking.
Step 9: Once the noodles are cooked, stir in the remaining 1 cup of shredded mozzarella cheese until melted and gooey.
Step 10: Ladle the hot Million-Dollar Cheesy Lasagna Soup into bowls.
Step 11: Top each serving with a generous dollop of the prepared ricotta cheese mixture. Garnish with extra grated Parmesan cheese and fresh basil leaves, if desired. Serve immediately.