Make the chicken stock: To a large stock pot add 3 liters of water, the chicken back/carcass, the onion, celery, leek carrots and herbs. Let simmer for 90 minutes to 2 hours.

Sieve the broth, discard of the carcass and boiled vegetables.

Add butter to a new pot, add the chicken, brown for a few minutes and top with the chicken stock just covered then simmer for 20 minutes on medium heat until the chicken is cooked through.

Remove the cooked chicken from the pot, remove the skin and if desired, removed the meat from the bone and set aside.

Boil the stock on high heat until it has reduced by at least 1/3 then add the sliced potatoes into the pot and cook for 15-20 minutes until tender.

While that simmers, add a tablespoon of butter to a frying pan and add the finely minced leek and carrots in the pan and sauté them for a few minutes until they start to brown.

To finish, turn off the heat, then add the cooked leeks and carrots and the reserved chicken meat to the stock and potatoes and then fill a bowl with the cream and egg yolk. Whisk them and add in 1-2 ladles of chicken stock, slowly so it does not curdle.

Continue adding stock until the cream is warm then pour all the cream-yolk mixture into the pot.