Stock: Place the chicken in a pot of water, covering the chicken entirely. Add 2 carrots, 2 celery stalks, and 1 onion, cut into approximately 1-inch pieces. Add parsley, thyme and a bay leaf and bring to a boil. Turn the heat to medium low and cook until chicken is cooked, about 20-30 minutes. Add salt and pepper, to taste.
Cut the remaining carrots, celery, onions into 1-inch sticks and place them in a saucepan with water to cover. Cut the leeks into 1-inch sticks, slice the mushrooms and add to saucepan. Parboil vegetables in salted water about 15 minutes. Take out the chicken when poached (no red color must be seen under the skin) and discard vegetables from stock. Strain the chicken stock through a strainer. Remove the skin from the chicken and cut chicken into 8 pieces. Put the chicken and the parboiled vegetables into the stock. Mix the egg yolks with the cream and add to the stock. Add the lemon juice and butter. Season with salt, pepper and nutmeg.
I cook the second set of vegs. in the chicken stock to give more flavor. You could use canned chicken broth too.
Serve in soup plates with boiled potatoes or white steamed rice. Enjoy!