Boil the Pasta: Drop the dry pasta shells into a large pot of fiercely boiling, salted water. Cook according to the package directions (about 8 minutes) until al dente (firm in the center). Drain thoroughly and set aside.
Sear the Meat: While the pasta boils, drop the raw ground beef and diced yellow onions directly into a large, dry skillet over medium-high heat. Let the meat sizzle and violently brown for exactly 6 minutes, breaking it apart with a wooden spoon.
Bloom the Spices: Once the beef develops a sticky, dark crust, stir in the freshly minced garlic and dry Italian seasoning. Cook for exactly 60 seconds until highly aromatic.
Build the Sauce: Aggressively pour the warm beef broth and smooth tomato sauce into the hot skillet. Use your wooden spoon to scrape up all the deeply browned, savory bits hiding on the bottom of the pan.
Add the Cream: Lower the heat to medium-low. Gently stir the heavy whipping cream completely into the red sauce. Let the incredibly rich liquid gently simmer for exactly 3 minutes.
Melt the Cheese: Pull the bubbling skillet entirely off the hot stove. Scatter the freshly grated sharp cheddar across the liquid, fiercely stirring until the gravy becomes remarkably glossy and completely smooth.
Combine and Serve: Dump the drained pasta shells entirely into the hot cheese sauce. Vigorously toss the heavy mixture until every single noodle is smothered in the meat gravy. Serve immediately!