Combine broth, water, potatoes, onion, celery, pepper and half the
salt. Cover and boil until potatoes are soft, (about 20 min). As the
potatoes cook, break the egg in a small bowl, mix with fork, add
remaining salt, and add the flour gradually mixing with a fork,
cutting the flour into the egg as it makes ribbles that resemble small
pieces of noodles. Add a little more flour if the mixture is too wet
to break into ribbles. When the potatoes are soft, add one and a half
cups of milk. Bring back to a boil and sprinkle the ribbles into the
potatoes, breaking up with fingers as necessary as you sprinkle. Stir
and let simmer, uncovered, for about 5 minutes. Makes about 5 Cups.