In a large pot set over medium-high heat, brown the ground beef and Italian sausage. While cooking, season with salt and pepper, then drain the excess fat and set the meat aside.
Return the pot to the stove and warm the olive oil over medium heat. Add the chopped onion and sauté for approximately 5 minutes, stirring now and then. Incorporate the minced garlic and continue to cook for another 1 to 2 minutes.
Mix in the tomato paste, marinara sauce, red pepper flakes, oregano, basil, parsley, and broth. Return the browned meat to the pot and stir thoroughly.
Bring the mixture to a boil. Add the broken lasagna noodles, reduce the heat to medium-low, and cook, stirring occasionally, until the noodles become tender. Stir in the spinach, if using.
In a small mixing bowl, combine the ricotta, mozzarella, and Parmesan cheeses.
To serve, ladle the soup into bowls and top each serving with a generous spoonful of the cheese mixture. Garnish with fresh basil.