Cook the potatoes in their skins until nearly soft. Peel and slice thinly. Slice the onions thinly across and cook them slowly in the butter in a frying-pan until just golden coloured. Remove the onions and keep them hot. Toss the potatoes in the fat as for Sauté Potatoes. Add the onions to them and mix. Season well with salt and pepper. Serve in a hot dish and sprinkle with chopped parsley.