Slice the cooked potatoes and the meat. Peel and slice the onions. Peel, core and slice the apples. Melt the butter and fry the onions and apples until golden-brown. Arrange layers of potatoes, meat, apples and onions in an ovenproof dish, seasoning the layers with salt and pepper and nutmeg. Pour on the stock and dot the top with a little butter. Bake at 350°F, 180°C, gas mark 4 for about forty-five minutes until golden brown.