Don't miss out on our special Christmas issue with free 2023 calendar - subscribe by 11 October!
Put the chicken in a large pan with the bay, half the thyme sprigs, the parsley stalks, onions, garlic, stock and seasoning. Pour the milk over the chicken and, if you need to, top up with water to make sure the chicken is covered. Bring the chicken to the boil, then turn down and simmer for 15 mins. Lift from the liquid and leave to cool.
Drain the poaching liquid through a sieve into a large jug – you need 650ml to make the sauce for your pie.
Meanwhile, heat the butter in a saucepan over a low-medium heat. Add the leeks and the mushrooms, and cook for 5-10 mins until soft, then season well. Add the flour and stir to coat the vegetables. Slowly add the poaching liquid, stirring until you have a thick sauce.
Using two forks, pull the chicken apart into thumb-sized chunks rather than chopping it – I feel you get a far better pie this way. Chop the parsley leaves, then stir into the leeks with the thyme leaves, crème frâiche and chicken. Check the seasoning, then spoon the mixture into your pie dish (or dishes) to cool slightly.
Heat oven to 220C/200C fan/gas 7. Roll out the pastry on a lightly dusted work surface to the thickness of a £1 coin. Cut thin strips from the edges and use a little water to stick these around the lip of the pie dish, then wet the top of the pastry strip. Lift the pastry on top of the pie, trim the edges and crimp them with your fingers or a fork. Brush the top with milk and cut a steam hole in the middle.
Put the dish on a baking sheet and cook in the oven for 20-25 mins until the pastry is risen and golden. Some of the filling will have bubbled up through the steam hole. Have a bottle of tomato ketchup on hand to serve, if you like – and be careful, the pie will be hot.