In a large enameled pot set over medium-high heat, brown the ground beef and Italian sausage, seasoning with salt and pepper. Once fully cooked, drain the excess fat and transfer the meat to a separate dish.
In the same pot, warm olive oil over medium heat. Add the chopped onion and sauté for approximately 5 minutes until softened, stirring occasionally. Introduce the minced garlic and continue cooking for an additional 1–2 minutes.
Incorporate the tomato paste, marinara sauce, crushed red pepper flakes, oregano, basil, and chopped parsley into the pot. Pour in the broth and reintroduce the browned meat mixture. Stir to combine.
Raise the heat to bring the soup to a boil. Add the broken lasagna noodles and then reduce the heat to medium-low. Simmer gently, stirring intermittently, until the noodles are al dente and tender. Add spinach during the final minutes of cooking, if using.
Meanwhile, in a small mixing bowl, blend together the ricotta, mozzarella, and Parmesan cheeses until evenly mixed.
Serve the hot soup in individual bowls, topping each with a generous spoonful of the cheese mixture. Garnish with fresh basil leaves before serving.