Rinse the chicken under running water. inside and out. Remove any chunks of fat from the cavity. then place the chicken into a large saucepan along with the parsley sprigs, carrot and barley or rice. Fill the pan with water and bring to the boil. Skim away any foam that rises to the surface. Add the salt and reduce the heat to low. Allow to simmer gently for 2 hours. or until the meat is falling from the bones of the chicken.
Remove the chicken from the stock. then strain the stock through a colander which is positioned over a large bowl. Skim any fat from the surface of the stock. Clean the saucepan and return it to the stove. Add the butter and saute the leek until soft. Pour in the strained chicken stock, add the potato and continue to cook over medium heat for 8-10 minutes, or until the potato is tender when pierced with a skewer.
Meanwhile. remove and roughly chop the chicken flesh. discarding any skin. A few minutes before you are ready to serve, return the chicken meat to the soup along with the roughly chopped parsley. Season to taste with sea salt.