Bring the water with the lentils to the boil, add the diced onion and baking soda. Let simmer for 30 minutes.
In the meantime, stir the ingredients for the sparrows into a thick batter. Now cut off the dough with a teaspoon and add it to the soup. Let simmer for another 10 minutes.
Finally, season the soup to taste with salt and vinegar. If you like, you can add chopped wiener sausages.