In a large slow cooker, combine the sausage, onion, garlic, oregano, red pepper flakes, tomato paste, diced tomatoes, bat leaves, and broth.
Cook on low for 8-9 hours.
During the last 30 minutes of cooking, add in pasta.
When ready to serve, preheat broiler. Dish up soup into oven-proof bowls.
Top each bowl with a spoonful of ricotta and a sprinkling of shredded mozzarella.
Place under broiler for 3-5 minutes or until cheese is hot and melted.