To make the stock, preheat the oven to 400 degrees farenheit. Put the chicken wings, onion and leek in a roasting pan and roast in the oven for about 23 min until golden brown. Discard any residual fat in the pan and pour 350ml/ 12fl oz/ 1 1/2 cups of the water. Place the pan on top of the stove and bring the liquid to the boil, stirring all the time to incorporate the residue on the bottoom of the pan.
Transfer both the chicken and pan juices to a clean pan. Top up with the remaining water and add the vegetables. Bring to the boil then reduce the heat and simmer for 40 min minutes to 1 hour. Strain the juices into a jug. (This should yield about 1 litre / 4 cups of stock.
To make the soup, heat the butter in a large pan, add the leek, shallot and mushrooms and fry until the beginning to soften. Stir in the flour and cook over low heat for 30 seconds. Add about 1/3 of the stock and, stirring all the time bring to the boil. Reduce the heat and simmer for 3-4 minutes, then add the remaining stock. Season the soup to taste with salt and pepper.
Stir the cream and chopped parsley into the soup and heat gently. Pour into individual serving bowls and serve hot.