Preparation: thinly slice the spanish onions and grate the potatoes and : parmesan cheese. Heat the oil in a heavy based pan. Add the onions and cook over a medium heat until they are tender. Add the water and wine and simmer for 20 minutes or until the liquid has evaporated and the onions are a dark-reddish brown. Combine the rosemary, potatoes, flour, yoghurt, egg and parmesan cheese. Add the onions. Spread the mixture evenly into a well-greased 25cm ovenproof flan dish. Bake at 200C for 35-40 minutes until golden brown. Sprinkle with parsley, then cut into wedges and serve.