Boil the potatoes in their skins, peel and cut them into 1-inch cubes. Chop cashew nuts and fry in oil until golden. Drain and set aside. In the same pan fry the vermicelli until golden, then drain and set aside. Fry the mustard seeds and, when spluttering, add the onions and fry for five minutes. Stir in the flour, add the water and bring to the boil. Add potatoes, vermicelli, cashew nuts, spices, bay leaves and salt. Stir and simmer till the vermicelli is cooked and water evaporated. Remove from the heat and serve after five minutes.