Brown Italian Sausage: In a large pot or Dutch oven, cook the Italian sausage over medium heat, breaking it into smaller pieces with a spoon, until browned and cooked through. Remove any excess fat.
Sauté Aromatics: Add diced onion, minced garlic, diced carrots, and diced celery to the pot with the cooked sausage. Sauté for 5-7 minutes, or until the vegetables are softened and aromatic.
Simmer Soup: Pour in the chicken broth and diced tomatoes with their juices. Add dried basil, dried oregano, and red pepper flakes if using. Bring the soup to a simmer and let it cook for 15-20 minutes to allow the flavors to meld.
Add Cream and Cheese: Stir in the heavy cream and grated Parmesan cheese until the cheese is melted and the soup is creamy. Season with salt and pepper to taste.
Serve: Ladle the Creamy Parmesan Italian Sausage Soup into bowls and garnish with chopped fresh parsley, if desired. Serve hot with crusty bread or garlic toast for dipping.
