Place the chicken in a large stockpot and cover with water. Bring to the boil and skim off any impurities.
Reduce to a very low heat and add the vegetables, bouquet garni and season lightly. Simmer gently for 1½ - 2 hours.
Skim off the fat and strain off the stock. Discard the vegetables.
Take the meat off the carcass and set aside.
For the soup
Heat the stock in a pan and add the carrots and leeks and cook until just tender. Add the shredded chicken and season.
To serve, ladle into deep bowls and scatter with parsley.
Freezing and defrosting guidelines
Make the soup, then leave to cool at room temperature. Freeze (without garnishes or toppings) in a rigid container, leaving a bit of space for expansion, for up to 1-3 months. Reheat either from frozen or defrost in the fridge overnight. Once piping hot, add toppings or garnishes and serve.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.