Mix the butter into the hot mashed potatoes, add a good pinch of salt, and the flour, and mix well, then add enough milk to make a soft, slack dough. Roll out and line a 1-qt bowl with some of it, reserving enough for the lid. Fill with the apples, peeled and cored and finely sliced, and sweeten to taste with sugar. Add 2 whole cloves, the lemon juice and the cider (or water), taking care not to make it too wet. Dampen the pastry edges, lay the lid on and press down. Cover with foil and secure well. Steam, or cook set in boiling water up to the rim, for 2 2 1/2 hours. Serve cut in wedges with cream or home-made custard.