In a large pot, over medium heat, add the olive oil and onion and sauté until the onion is translucent.
Add the sausage, breaking it up with a wooden spoon, and cook it until it is no longer pink.
Add the pasta, broth, crushed tomatoes, Italian seasoning, salt and pepper, and bring the pot to a boil.
Cook for about 10 minutes at a low boil until the pasta is al dente, making sure to stir the pot occasionally so the pasta does not stick to the bottom.
Remove the pot from heat and add the heavy cream and ¾ cup mozzarella cheese, stirring to combine.
Serve with the remaining mozzarella cheese sprinkled on top of each person's dish.