Philly Cheesesteak Stuffed Shells

1 pound lean ground beef
2 tablespoons butter
1 small yellow onion, diced
1 small green bell pepper, diced
2 tablespoons ketchup
1 tablespoon Worcestershire sauce
1/2 teaspoon Kosher salt
1/2 teaspoon fresh ground black pepper
8 ounces cheddar cheese, cut into small cubes (divided)
24 jumbo pasta shells, cooked
1 tablespoon cornstarch
1 cup milk (I used whole)
1 cup beef broth

Preheat the oven to 350 degrees.
Add the ground beef to a large cast iron skillet (this browns very well) and brown until a deep brown crust appears before breaking the beef apart.
Stir the ground beef and brown until a deep crust appears on about 50 or so percent of the beef.
Remove the beef (you can leave the fat) and add the butter and the onions and bell peppers.
Let brown for 1-2 minutes before stirring, then let brown for another 1-2 minutes before stirring again.
Add the beef back into the pan.
Add the ketchup, Worcestershire sauce, salt and black pepper into the pan and stir.
Take it off the heat and scoop it into the pasta shells.
Top each shell with cubes of cheese (use half the cheese for this).
Using the same pan add the beef broth, milk and cornstarch and whisk before turning the heat back on.
Add in the rest of the cheddar cheese a little at a time while whisking for 3-5 minutes or until thickened.
Pour about half the sauce around the shells.
Bake in the oven f0r 10 minutes to melt the cheese.
Serve with the remaining sauce.