**Cook the pasta**
- Bring a large pot of salted water to a boil.
- Add the pasta shells and cook according to package instructions until al dente.
- Reserve 1/2 cup of pasta water, then drain and set the shells aside.
**Brown the beef**
- In a large skillet over medium-high heat, warm the olive oil (if using).
- Add the ground beef and diced onion. Cook, breaking up the meat with a wooden spoon, until the beef is browned and the onions are softened, about 5–7 minutes.
- Drain any excess fat if necessary.
**Add garlic and seasonings**
- Stir in the minced garlic and Italian seasoning (if using). Cook for 1 minute until fragrant.
- Season with salt and pepper to taste.
**Stir in liquids**
- Reduce the heat to medium. Add the tomato sauce and beef broth, stirring to combine.
- Bring the mixture to a gentle simmer and let it cook for 5 minutes to slightly reduce the sauce.
**Make it creamy**
- Stir in the heavy cream (or half-and-half). Let the sauce simmer for another 2–3 minutes.
- Add a splash of reserved pasta water if the sauce seems too thick.
**Combine with pasta and cheese**
- Add the cooked pasta shells to the skillet, tossing to coat them in the sauce.
- Stir in the shredded cheese until melted and creamy. Taste and adjust seasonings if needed.
**Serve**
- Garnish with chopped parsley or grated Parmesan if desired.
- Serve hot with a side salad, garlic bread, or steamed vegetables.