For the potato soup, wash the leeks and cut into small rings. Peel the potatoes and cut into small cubes. Put everything together in a tall, unperforated steamer basket and pour in the soup.
Place in the steamer at 100 °C for 15 minutes. If the potatoes are coarser cut, simply 2 minutes longer. Then, using a blender, finely mash everything.
Stir the whipped cream and the spices, as well as the herbs into the soup. Again at 100 °C for 3 minutes in the steamer.
To serve, either place herbs in the center of the plate on top of the soup or place a dollop of sour cream (or whipped cream) on top.