Peel, wash and cut the potatoes into pieces. Peel garlic and onion and chop finely. Melt the fat in a saucepan. Sauté onion and garlic in it while stirring until transparent. Add the potatoes and steam briefly.
Deglaze with wine. Bring to the boil. Add stock and cream and simmer at low heat for about 15 minutes.
In the meantime, wash the herbs, shake them dry and pluck the leaves from the stems. Set aside some chervil for garnishing. Add the herbs to the soup, puree the soup finely. Season to taste with salt, pepper and nutmeg.
Mix sour cream and lemon juice, season with salt and pepper. Arrange soup in bowls, spread lemon sour cream on top, garnish with cress and chervil. Sprinkle with 1 tsp. olive oil and sprinkle with coarse pepper.