Soak the lentils in water, rinse them, bring to the boil in approx. 2.5 - 3 liters of water and simmer on a low flame for approx. 25 minutes.
Start the other preparations in parallel. Peel and dice the potatoes. Clean and dice the parsnips and carrots.
Add everything to the lentils after approx. 25 minutes. Depending on your taste, the potatoes can also be added a little earlier. Add a little vinegar and salt. Cut the leek into rings and also add to the soup. Let the soup simmer for about 15-20 minutes.
Cut the onions, dice the smoked tofu and fry both in a pan.
After approx. 15-20 minutes add the onions and tofu to the soup. Simmer the soup for approx. 5 minutes and season with a little pepper, more salt and a lot more vinegar, as well as with the fresh or dried marjoram.