West Country Chicken & Ham Pie

Serves 4

60g butter
3 leeks, cleaned and sliced
60g flour, plus more to dust
425ml milk
salt and pepper
1tsp english mustard
300g leftover cooked chicken, cut into chunks
150g cooked ham, cut into chunks
1tbsp flat leaf parsley
freshly grated nutmeg
flour for rolling
300g puff pastry
1 egg yolk, mixed with a little water and salt

Melt the butter in a heavy pan and add the leeks and cook gently for 5 mins.  Pour in a splash of water, reduce the heat, cover and sweat for 10 mins.  Add the flour and stir for 1 min.
Take the pan off the heat and gradually add the milk.  Return to the heat and bring to the boil, stirring; reduce the heat and simmer for 5 mins.  Season, add the mustard, chicken and ham. Heat through then add the parsley and nutmeg to taste.  Set aside and leave to cool a little.
Preheat the oven to 200, gas mark 6.  Spoon the chicken into a pie dish.  On a floured surface, roll the pastry out to the thickness of a 50p piece.
Cut off a strip of pastry, wet it and place it on the lip of the pie dish.  Lay the rest of the pastry on top, pressing down firmly.  Trim off the excess.
Crimp the edges and use pastry scraps to decorate.  Make 3 cuts in the middle to let the steam escape.
Brush with the egg yolk and bake for 30-40 mins, or until golden.