Peel the onion, dice finely. Peel and wash the potatoes and cut into small cubes. Heat the butter in a saucepan and sauté the onions until translucent. Briefly sauté the potatoes. Pour in the stock, cover and simmer over low heat for approx. 10 minutes.
Clean and clean mushrooms, cut into thin slices. Pour into the broth, cover and simmer over low heat for approx. 20 minutes.
Whisk egg yolks with sour cream. Pull the soup off the stove. Stir in the egg cream, season with salt and pepper, sprinkle with dill tips and serve.