Preheat your oven to 350°F (175°C).

In a large skillet, brown the ground beef over medium heat for about 6-8 minutes. Remove and set aside.

In the same skillet, add butter, then sauté diced onion and bell pepper for about 4 minutes.

Return the beef to the skillet and add ketchup, Worcestershire sauce, salt, and black pepper. Mix well and cook for 2 minutes, then add half of the cheddar cheese until melted.

Cook jumbo pasta shells according to package instructions until al dente, drain and cool slightly, then fill with the beef mixture.

In the same skillet, whisk together beef broth and milk, adding cornstarch gradually. Cook until sauce thickens, then mix in the remaining cheddar cheese until melted.

Spread half of the cheese sauce in a baking dish, arrange the stuffed shells, and pour the remaining sauce on top. Bake for 10 minutes until cheese is bubbling.

Remove from oven and drizzle any remaining sauce over the shells before serving.