For the potato-leek soup, finely dice onion and heat oil in a pot, slowly brown onions over medium heat. In the meantime, peel the potatoes and cut into approx. 2 x 2 cm cubes, add to the onions, fry a little.
Then pour in the water. Now add soup vegetables and marjoram, as well as salt, pepper, caraway seeds and the cleaned sliced leek (set aside some of the leek for decoration), and simmer the soup for half an hour.
Puree with a blender or pass through a sieve and taste. Finely chop the remaining leek and sprinkle into the potato-leek soup before serving.