Wash and scrub the potatoes leaving them unpeeled. Boil the potatoes in lightly salted boiling water until they are tender. Drain and set aside the potatoes in a hot saucepan to dry in their steam. Once cooled, start to peel them. Mash the potatoes coarsely then add the peas and cooked Parma ham and combine. Season with salt and freshly ground pepper, pour in the melted butter. Add some plain flour and make into a potato cake, rolling on a lightly floured board to form a round shape of about 1cm thickness. Cook on a hot dry griddle or dry frying pan until the potato cake is crisp. Serve with salad leaves and a drizzle of olive oil.