Preheat the oven to 220°C (425°F) mark 7.
Melt the butter in a heavy based pan and add the flour off the heat. Whisk in the turkey stock and cook over a medium heat, stirring all the time until the sauce is smooth. Season well and add the mustard.
Place the turkey pieces, ham and leeks in the bottom of an oval pie dish, sprinkle with the fresh parsley and pour over the sauce.
Roll out the pastry on a lightly floured surface and cover the pie dish with the pastry. Brush the top of the pastry with a little beaten egg and bake in the oven for 20-25 minutes. After this time reduce the heat to 180°C (350°F) mark 4 and bake for a further 15 minutes.
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