Layer up potatoes, turkey, and lumps of stuffing, (in that order), putting a tiny knob of butter and a scant sprinkling of S& P onto the potatoes with each layer.
Save a layer of potatoes for the top.
Pour gravy (possibly thinned down a bit) over all, until it only just covers, and then add the reserved layer of potatoes.
Put a knob of butter and some S& P onto each potato.
Cover casserole with foil (or a lid) and bake in a low oven for about an hour (longer if you have done a large hotpot)- make sure the potatoes are cooked by inserting a knife to see if they are tender.
Serve with cabbage, brussels sprouts, carrots- whatever veg you like, and, for the piggies amongst us, some crusty bread.