Chop bacon fine and fry in skillet until crisp and brown. Put cooked bacon in large saucepan and add potatoes, onions, celery, salt and pepper. Cover with water and cook until vegetables are tender, about 25 minutes. Put noodles (or rivels) into gently boiling soup, stirring constantly so they stay separate. Add milk and butter; cook 10-15 minutes more, or until noodles are done. To make rivels: Pour 1 c. all-purpose flour onto flat surface (cutting board). Make a well in the center and add 1 egg, slightly beaten and 1 tsp. salt. Using your hands and a knife, work these 3 ingredients together into a noodle-type pastry. Knead once or twice; chop into small pieces and to gently boiling soup. Makes 6-8 servings.