01 -
Preheat the oven to 350 degrees Fahrenheit.
02 -
Add the ground beef to a large cast iron skillet and brown until a deep brown crust appears before breaking the beef apart. Continue browning until about 50% of the beef develops a crust.
03 -
Remove the beef from the skillet, leaving the fat in the pan. Add the butter, onions, and bell peppers. Cook for 1-2 minutes without stirring, then stir and brown for another 1-2 minutes.
04 -
Return the beef to the skillet and add ketchup, Worcestershire sauce, salt, and black pepper. Stir to combine, then remove from heat.
05 -
Spoon the beef mixture into the cooked pasta shells. Top each shell with half of the cheddar cheese cubes.
06 -
In the same skillet, whisk together the beef broth, milk, and cornstarch. Heat the mixture and add the remaining cheddar cheese in small amounts, whisking continuously for 3-5 minutes until the sauce thickens.
07 -
Pour half of the sauce around the stuffed shells in a baking dish, then bake for 10 minutes or until the cheese melts.
08 -
Serve the stuffed shells with the remaining sauce drizzled on top.