Step 1: Heat the olive oil in a large Dutch oven or heavy-bottomed pot over medium heat. Add the Italian sausage, breaking it up with a spoon, and cook until browned and no longer pink. Drain off any excess grease, leaving about a tablespoon in the pot.
Step 2: Add the diced onion to the pot and cook until softened, about 5-7 minutes. Stir in the minced garlic, dried oregano, dried basil, and red pepper flakes (if using). Cook for another minute until fragrant, being careful not to burn the garlic.
Step 3: Pour in the crushed tomatoes, tomato sauce, and chicken or vegetable broth. Bring the mixture to a simmer, then reduce the heat to low, cover, and let it cook for at least 15-20 minutes, allowing the flavors to meld.
Step 4: If using heavy cream, stir it in now. Taste the soup and season with salt and pepper as needed.
Step 5: Add the broken lasagna noodles to the simmering soup. Cook, stirring occasionally, until the noodles are al dente, about 10-12 minutes, or according to package directions.
Step 6: While the noodles cook, combine the ricotta cheese, 1/4 cup of Parmesan cheese, and a pinch of salt and pepper in a small bowl.
Step 7: Once the noodles are cooked, turn off the heat. Stir in the shredded mozzarella cheese until it’s melted and gooey. Serve hot, ladling into bowls. Top each serving with a generous dollop of the ricotta mixture, a sprinkle of the remaining Parmesan cheese, and fresh chopped parsley.