Put the lentils in a suitable bowl, cover with cold water and soak for one night.
The following day, remove the peel from the onion, chop finely and sauté briefly in the oil. Drain the lentils in a sieve, add to the onions. Add the tomato puree and fill up with the vegetable broth. Peel the potatoes, cut into small pieces and stir in. Season the soup, bring to a boil and simmer with the lid on low heat for about 25 min.
Cut the chives into fine rolls and stir in at the end. Season the soup with the balsamic vinegar.
Our tip: Fresh chives are much more aromatic than dried ones!