Chop the onion and sweat in butter until translucent. Peel the potatoes, cut into cubes and sauté briefly. Pour in the water, bring to the boil, stir in the vegetable stock and pour the cream on top.
Simmer for 20-30 minutes until the potatoes are cooked and then puree everything.
Season the soup with salt, pepper, sugar and marjoram as desired and season to taste.