Add the ground beef to the pot with the onions and garlic. Season with salt, pepper, and Italian seasoning. Cook until the beef is browned and cooked through, about 6-8 minutes. Drain any excess fat if necessary.
Stir in the tomato sauce and tomato paste, mixing well to combine. Pour in the chicken stock and bring to a gentle simmer, allowing the flavors to meld together. Adjust the consistency with more stock if desired.
Lower the heat and slowly stir in the heavy cream, allowing it to come to a gentle simmer. Add the grated parmesan cheese and mix until melted and fully incorporated.
Fold the cooked shell pasta into the sauce, tossing gently to coat each shell evenly in the sauce. Warm through for a couple of minutes.
Remove from heat and sprinkle with fresh parsley. Serve warm, offering some extra parmesan on the side.