Brown the Sausage: In a large Dutch oven or heavy-bottomed pot, cook the Italian sausage over medium-high heat, breaking it up with a spoon, until browned and cooked through (about 5-7 minutes). Use a slotted spoon to remove the sausage, leaving about 1 tablespoon of drippings in the pot.
Sauté Aromatics: Add the diced onion to the pot and cook until softened, about 5 minutes. Add the minced garlic and tomato paste and cook for 1 more minute until fragrant.
Simmer the Soup: Return the cooked sausage to the pot. Add the crushed tomatoes, broth, oregano, basil, and red pepper flakes. Season with salt and pepper. Bring to a boil, then reduce heat and let it simmer for 20 minutes to allow the flavors to meld.
Cook the Pasta: Increase the heat to a medium boil and add the pasta. Cook according to package directions until al dente.
Prepare the Topping: While the pasta cooks, in a small bowl, combine the ricotta, mozzarella, Parmesan, and a pinch of salt and pepper.
Serve: Ladle the hot soup into bowls. Top each serving with a generous dollop of the cheesy mixture and garnish with fresh basil if desired.
