In rural Ohio, rivel soup is a treasured home-style soup and everybody has their own version. This recipe is from my mother.
You can add left over mashed potatoes after you have cooked the rivels in the onions and celery for extra potato flavor.
Cook potatoes, onions, celery, salt, dash pepper in 2 cups of water in stockpot. Cover and cook until potatoes are easily pierced with tip of knife.
To make rivels: beat egg and salt with fork in medium bowl. Add flour all at once and beat until small pebbles form. Use your fingers to break apart if necessary. If you have flour that did not incorporate into the egg, then just add it with the rivels as it will help thicken the soup.
Add uncooked rivels slowly, adding water if necessary, stirring constantly, approximately five minutes until tender. Add whole milk and crisp bacon and bacon grease. Add evaporated milk and simmer until flavors are well blended.