Heat a large deep skillet or Dutch oven over medium-high heat. Add the ground beef and diced onion. Cook for 5 to 6 minutes, breaking the beef into bite-sized morsels with a wooden spoon, until deeply browned and caramelized. Drain off any excess grease, leaving about 1 tablespoon in the pan.

Add minced garlic, Italian seasoning, smoked paprika, salt, black pepper, and tomato paste. Sauté for 60 seconds until fragrant, stirring constantly so the garlic does not burn. The tomato paste will coat the beef and deepen into a rich rust-red fond.

Pour in the beef bone broth, Worcestershire sauce, and dry pasta shells. Stir well, pressing the pasta down so it is submerged in the liquid. Bring to a rapid rolling boil, then reduce heat to medium-low, cover with a tight-fitting lid, and simmer for 10 to 12 minutes, stirring twice to prevent sticking, until the pasta is tender and most of the liquid is absorbed into a glossy sauce.

Remove the lid. Stir in the butter and heavy cream over low heat until the butter melts and emulsifies with the natural pasta starches into a silky gravy. Turn off the heat and fold in the grated parmesan and white cheddar until luxuriously melted and creamy.

Let rest for 2 minutes to allow the sauce to settle into the pasta shells. Garnish generously with fresh chopped parsley and extra cracked black pepper. Ladle into warm dinner bowls and serve immediately.