Directions

1. Put the chicken in a pan, which is large enough to take it snugly. Roughly chop the carrot, onion and celery and tuck around the chicken with the bouquet garni. Pour in enough water to come just over halfway up the chicken, then season with salt and pepper.
2. Bring to the boil, then reduce the heat, cover tightly and simmer gently for 1-1 1/4 hrs, until the chicken is well cooked. Carefully lift the chicken out onto a board lined with kitchen paper to absorb any stock that leaks out. Then strain the stock, discarding the veggies, and measure 500ml into a jug - any extra you can cool and freeze for another time.
3. Heat the oven to 200C/fan 180C/gas 6. Strip the meat from the chicken, discarding the skin and bones. Cut the meat into large chunks and put into a 1-litre pie dish.
4. Melt the butter in a pan, add the leeks and fry until starting to soften. Sift in the flour and cook for 1 min. Gradually stir in the stock, cooking until the sauce is smooth and glossy. Take off the heat and add lemon, parsley and creme fraiche. Season. Pour the sauce over the chicken and leave to cool.
5. Roll out the pastry and trim to 5cm larger than the pie dish. Brush the edge of the dish with water. Lay the pastry on the pie, tucking the edges under to make a double layer around the rim. Press the pastry edge to seal it. Roll out any trimmings to make leaves for the top. Brush the pastry with milk or egg and bake for 30-35 mins until the pastry is golden.