Bring a pot of water to a boil and cook penne until just tender, then drain and set aside.

In a large pot, cook sausage with onion and garlic over medium heat until browned.

Add chicken broth, crushed tomatoes, diced tomatoes, pasta sauce, Italian seasoning, and red pepper flakes, then simmer.

Pour in cream, add butter, mozzarella, and Parmesan, stirring until melted and creamy.

Simmer for 10 to 12 minutes, stirring occasionally.

Remove from heat and stir in remaining mozzarella.

Add cooked pasta, stir well, and serve hot.