Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9x5 inch loaf pan.

In a large bowl, stir together the bread and milk. Add the beef, pork, egg yolk, onion, salt, ground black pepper, dry mustard, sage, celery salt, garlic salt and Worcestershire sauce. Mix well and set aside.

To make filling, in a medium bowl combine the egg white and water. Toss lightly with the bread pieces and Cheddar cheese.

Pat 1/2 of the meat mixture into the prepared loaf pan. Cover with the cheese filling and top with the remaining meat mixture.

Bake in the preheated oven for 1 1/2 hours.