Peel and finely chop the onion. Clean and wash the zucchini and possibly cut off some slices to garnish. Peel and wash the potatoes. Chop zucchini and potatoes coarsely
Fry the onion in hot oil. Briefly fry the potatoes and courgettes. Add a good 1/4 l water and stock. Bring everything to the boil, cover and cook for about 15 minutes
Wash the chervil and add to the soup, except for a few leaves. Remove the soup from the stove and puree. Season to taste with salt and pepper. Stir in sour cream. Garnish with zucchini slices, chervil and lemon balm