Wash lentils well and rinse well. Cover with 5 cups of water. Bring to a boil. Reduce heat to medium, & add carrots & celery and bacon. Simmer while caramelizing onion in butter in a separate frying pan. Add to soup when ready. Add vinegar, salt and pepper.
Cook until lentils are tender and soup has thickened a little. This will take approx. 20-30 minutes total cooking time.
Prepare egg dumplings while soup is cooking.
Beat 2 eggs well. Add flour and salt. If mixture is too thick, add some water until the consistency is like a thick gooey/elastic paste. When soup is ready, turn heat down to a very low simmer. Use a teaspoon and scoop out a heaping amount of the dumpling mixture and ease and/or drop it carefully into the soup. Do not stir the soup. When entire dumpling dough mixture is used up, once again, do not stir soup. Place a lid on the soup pot and let simmer for at least 5 minutes, or until the dumplings are cooked and firm.
Remove bacon and celery and serve soup immediately.
*** Serving suggestion(s): Add sliced (1/2 inch thick) Polish sausage or kielbasa sausage during the early cooking stage, if more meat is desired.
Serve with fresh/crusty French bread & butter (if desired). You can also adjust the apple cider vinegar by adding an extra splash of vinegar to individual servings/plates of the soup - according to taste. Tarragon vinegar is also a great choice.