For the chervil soup, peel the onions and potatoes.
Cut the potatoes into small pieces, chop the onions finely. Melt butter in a large saucepan and sauté onions and potatoes.
Add the vegetable soup and simmer in a closed saucepan over medium heat for about 15 minutes.
Coarsely chop the nuts and seeds and roast them in a dry frying pan without oil until they are fragrant.
Wash, dry and finely weigh the chervil.
Finely puree all ingredients in a saucepan and add the chervil. Bring everything to a boil and then reduce heat.
Mix the sour cream with the egg yolk and stir into the soup, which is no longer boiling.
Now serve the chervil soup and sprinkle with the roasted seeds and nuts.