Peel the potatoes, cut each one into 4 pieces and boil them for about 20 minutes. Cut the onion into rings. Heat the oil and fry the onions in it. When it is almost done, add the chopped ham. Mash the boiled potatoes very well.
Add the egg, flour, nutmeg, salt and olive oil. Knead for a decent amount of time to get a smooth dough. Grease a baking tray with oil. Divide the dough into 4 pieces and roll each one into a small sheet with a of about 7″ (18 cm). Place them in a tray.
Distribute tomato sauce, the fried ham and onions and finely chopped parsley on each crust. Sprinkle it with grated cheese, salt and black pepper. Bake in a moderate oven for about 20-30 minutes.