Steam the onions and frozen soup greens in the oil until translucent, deglaze with the vegetable stock, add the potato cubes and simmer for 15 minutes. Puree in the food processor, mix in the creme fraiche, season with marjoram, nutmeg and savory and season with salt and pepper. Bring the soup to the boil and let the cubes of Mettendchen steep in it.
Put 1 hot, peeled jacket potato in each plate, top up with hot soup and serve.