A hearty rustic chicken and vegetable soup. This soup is exactly the type of soup I crave when the weather is cold and the skies are grey. In the colder months a large pot of this was always on my granny's stove. If you are fat adverse you may like to skim the fat off as the chicken cooks. My granny never did this and neither do I but if it pleases you to do so then please do.
Soak the dried soup mix in cold water for at least 2 hours or overnight is best.
Slice the leek, peel and chop the carrot into small pieces and slice the celery. Place in a colander and rinse under cold water to remove any dirt.
Add the butter into a large pan, that is large enough to take all the vegetables and the whole chicken later. Over a low heat sweat the vegetables until they have softened slightly. Then place the chicken on top, if the chicken is trussed remove the string, which will help it cook quicker. Strain and discard the water the dried soup mix soaked in and place in the pan around the chicken along with the diced potatoes. Pour water over until it almost completely cover the chicken, don't worry if the breast isn't fully submerged it will cook in the steam. Season with sea salt. When the pan comes to the boil place a lid on the pan and turn the heat under the pan to it's lowest and cook until the chicken is cooked through. I find for this size chicken 45 - 50 minutes is enough but do check that the chicken is cooked through and cook for longer if using a larger chicken.
When chicken is just cooked through remove and transfer to a plate allow to cool for 15 - 20 minutes until cool enough to shred. Remove the skin and discard. Remove all the meat from the carcass and return it to the pan of soup. Season to taste with salt and pepper and serve with some crusty bread.