Start by browning the Italian sausage in a large soup pot or Dutch oven over medium heat. Break it up into smaller pieces as it cooks. Once the sausage is browned, remove any excess grease.
Add diced onions to the pot and cook for about 2-3 minutes until they become translucent. Stir in the minced garlic and sauté for another 30 seconds or until fragrant.
Pour in the chicken broth, diced tomatoes, dried basil, dried oregano, and red pepper flakes. Give it a good stir, and bring the mixture to a gentle boil.
Reduce the heat to low, cover the pot, and let the soup simmer for about 20-25 minutes, allowing the flavors to meld together.
Stir in the heavy cream and bring the soup back to a simmer. Be careful not to boil it vigorously; a gentle simmer is ideal.
Add the cheese tortellini to the simmering soup and cook them according to the package instructions, usually around 5-7 minutes. Ensure they're cooked to your desired level of tenderness.
Season the soup with salt and pepper to taste. Remember that the sausage and canned tomatoes may already add some saltiness to the dish, so be cautious with the salt.
Once the tortellini is cooked, and the soup is seasoned to your liking, it's ready to serve. Ladle the Creamy Sausage & Cheese Tortellini Soup into bowls and garnish with fresh basil or parsley if desired.
Serve hot, with a sprinkle of grated Parmesan cheese on top for that extra burst of cheesy goodness.