Heat the oven to 375°F. Grease 8 cups of a standard muffin pan.

Cook the macaroni according to the package directions until just tender. Drain it, then return it to the saucepan. Stir in the butter, milk, and 1/2 cup of the cheddar until the cheese melts and coats the pasta. Set aside.

In a mixing bowl, combine the ground beef, breadcrumbs, egg, onion, 1 tablespoon of the ketchup, Worcestershire sauce, salt, and pepper. Mix gently just until combined.

Divide the meat mixture into 8 portions. Press each portion into a muffin cup, then shape it around the bottom and sides to make a well. Divide the mac and cheese among the wells. Bring the meat mixture up around the filling to cover it, pinching the edges together.

Wrap one slice of bacon around the top edge of each meatloaf muffin. Brush the remaining tablespoon of ketchup over the bacon.

Bake for 25 to 30 minutes, until the meat is cooked through and the bacon is browned. If needed, broil for 1 to 2 minutes to crisp the bacon, watching closely. Let the muffins rest in the pan for 5 minutes before removing them.