Gently pound pocket portion of each chop to flatten. Melt butter in medium skillet over medium heat and saute 1/2 cup onion and mushrooms until onion is soft. Transfer mixture to a medium-sized mixing bowl; add toasted bread, parsley, caraway seeds, egg, salt and pepper. Fill each chop with one-fourth of the mixture. Close the pockets with toothpicks. In a large skillet, heat oil over high heat and quickly brown chops (about 5 minutes on each side). Reduce heat to low and continue cooking until tender (25-35 minutes). Transfer chops to platter, remove toothpicks and keep warm. Pour all but 1 TBS of fat from skillet. Add remaining 1/2 cup onion and cook for one minute. Add vinegar and chicken broth. Bring mixture to a boil and cook for 3 minutes. Pour over pork chops. 4 servings.