Finely chop the onion and sauté in the oil until softened.
Cut the chicken thighs into small pieces and add them to the pot with the onions. Brown the chicken until it's nicely colored.
Finely chop the remaining vegetables and add them to the pot with the onions and chicken. Cook for about two minutes, then pour in 3 liters (3 quarts) of water and add salt. Let the soup simmer over medium heat for 30 minutes.
In a separate bowl, whisk together an egg yolk with the sour cream and chopped garlic. Gradually stir in two to three ladles of the hot soup to temper the mixture.
Pour the cream mixture back into the pot and stir in some fresh parsley leaves.
Serve the soup hot, garnished with extra fresh parsley leaves. Enjoy!