Brown the Italian sausage in a large pot over medium heat, breaking it up with a spoon as it cooks. Once it is no longer pink, add the diced onion and cook for three minutes until it softens.
Stir in the minced garlic and cook for one minute until fragrant. Pour in the marinara sauce and beef broth, then add the Italian seasoning along with a pinch of salt and pepper.
Bring the soup to a gentle boil. Add the broken lasagna noodles and reduce the heat to a simmer. Cook for 12 to 15 minutes, stirring now and then, until the noodles are tender.
While the soup simmers, mix the ricotta and Parmesan in a small bowl. Taste and add a little salt if needed.
Ladle the hot soup into bowls and drop generous spoonfuls of the ricotta mixture on top of each serving.