For the pies:
Preheat the oven to 200ºC /gas mark 6.
Melt the butter in a large saucepan and gently cook the leek and thyme leaves until the leek has softened.Increase the heat, pour in the sherry and cream and bubble for a couple of minutes to thicken a little.
Take the chicken meat off the bone and tear into chunks or strips.
Add to the pan with the ham, mustard and chicken stock and season with salt and pepper.
Bring to a simmer and cook for a few minutes until the sauce has thickened slightly.
Spoon into one large or four individual pie dishes.
Brush the rim of each dish with the egg wash, cut the pastry into four (or leave whole if you are doing one larrge pie) and sit on top.
Press the edges down well to seal and trim off any excess pastry.
Cut a small slit in the top to let any steam escape and brush with the egg wash.
Bake for 15 minutes until the tops are golden and the sauce begins to ooze out of the dishes.
For the root veg mash:
Peel and chop the vegetables to roughly the same size chunks.
Place in a pan of salted water and bring to the boil.
Cook the vegetables until they are tender (about 20 minutes) and then drain well.
Return to the pan and allow the steam to evaporate for a minute before mashing with the butter, seasoning and mustard.
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