Peel, wash and chop the potatoes. Peel and chop onion and garlic. Heat the fat in a saucepan. Brown onion and garlic in it. Steam the potatoes briefly. Deglaze everything with wine and 3⁄4 l water.
Bring to the boil and stir in the stock. Cover and cook for about 15 minutes.
Wash the cress and cut from the bed. Approx. 3⁄4 Stir the cress into the soup. Puree everything finely. Stir in 100 g cream. Season to taste with salt, pepper and lemon juice. Arrange the soup with the crab meat, the rest of the cream in streaks and the remaining cress.