8  large cabbage leaves 21/2 cups diced cooked chicken 2  tablespoons chopped onion 1/2 cup finely chopped celery 1/4 pound chopped fresh mushrooms 1  small clove garlic, minced 1/2 teaspoon salt 1/2 teaspoon thyme leaves 1  egg, beaten 2  tablespoons butter or margarine 6  tablespoons flour 2  cups chicken broth 2  cups dairy sour cream [...]