Cut the potatoes in half lengthways and scoop out the centres (reserve this for soup). Parboil the potato shells for about 10 minutes in salted water, and while you are doing this prepare the tomatoes as stated above. Do the same with the peppers, only leave the skin intact and cook the pieces briefly in a little butter. Cut the ham into strips.
Oil a deep dish, fill the potato cases with the other vegetables and the ham, seasoning as you go, and pour a little melted butter over each. Cook in a moderate oven