Preparation

Place the chicken in a large pot with the onion, carrot, celery and parsley and cover with about 1.5ltr/3pts water. Bring to the boil, then gently simmer it for 1 hr or until the chicken is tender. Lift the chicken from the pan, cool slightly, then use a knife and fork to remove all the meat from the bones and skin. Reserve the meat and discard the bones and skin. Drain the stock and discard the vegetables. Return the stock to the heat and boil rapidly for 20 mins or until it is about a third of its original volume. Measure the stock - you should have about 600ml (1pt). This can all be done the previous day if you prefer. Preheat the oven to 220ºC (fan 200ºC/gas mark 7). Gently melt the butter in a pan, stir in the flour and let it bubble for a couple minutes.
Pour in the stock and bring to the boil, whisking all the time with a balloon whisk until the sauce thickens. Reduce the heat, stir in the mushrooms and leave to gently simmer for 4 mins. Season to taste. Cut the chicken into bite sized chunks and stir into the sauce with the parsley. Roll out the pastry on a lightly floured surface. Place a 1.4ltr/2½pt oval pie dish in the centre of the pastry, roughly cut around it. Now, cut strips of pastry from the pastry remaining around the edges of the dish. Brush the rim of the pie dish and attach the pastry strips to it. Spoon the chicken filling into the dish. Brush the pastry edges with water then lay the pastry on top. Trim the edges, then pinch them together to seal. Use any scraps of pastry to make decorations for the top, attaching them with water. Brush the top of the chicken pie all over with beaten egg. Make a steam hole in the centre of the pie. Place on a baking tray and bake for 25 mins or until the pastry is golden brown. Serve your hot chicken pie with creamed potatoes and buttered carrots.