Put the chicken in a large pot, cover it with the chicken stock and bring to the boil.
Take a slotted spoon and skim the froth from the top.Add the whole, unpeeled onion and the bay leaves. Season generously with coarse salt and freshly ground black pepper. Lower the heat right down and simmer for one hour
.Remove the chicken and set aside. Let it cool for a short time and then cut it up into large pieces. Carve off the legs, separating each of them into drumstick and thigh, and remove the breasts whole, carving them into two across the grain.
Turn up the heat under the pot to medium and add the leeks to cook until tender, about 5 - 8 minutes
Lower the heat right down again and return the chicken pieces to the pot to warm through for a few minutes.Discard the onion and bay leaves. Check seasoning and adjust if needed.
Lift the chicken and leeks out into warmed soup bowls. Ladle the broth over.