Make the filling well in advance (it freezes well) and best made a couple of days before. If freezing, unfreeze, bring to room temperature and put in a pie dish and cover with puff pastry and continue as above.
This braised pot pie also works well with beef – shin, chuck, skirt etc. or venison. If you just want a stew, serve with buttery polenta, mashed potato, creamy celeriac puree, savoy cabbage or wedges of roast pumpkin on the side.