Put the oil in a large frying pan and set over medium heat. When it is hot, put in the potatoes and fry them until they are golden and almost tender, about 10 minutes. Lift the potatoes out with a slotted spoon, and drain on paper towels. Turn the heat to medium-high, put in the cauliflower florets, and fry for 3 to 4 minutes, until they are golden brown. Lift the cauliflower out with a slotted spoon and drain on paper towels. Turn the heat off. Remove all the oil from the frying pan except for 2 tablespoons (the extra oil can be drained and reused). Turn the heat to medium-high and put in the ginger. Stir for 10 seconds. Now return the potatoes and cauliflower to the pan. Turn the heat down to medium. Put in the turmeric, salt, cayenne, cumin, and coriander. Stir gently to coat the vegetables with the spices. Add 3 tablespoons of water. Stir once and cover the pan. Turn the heat down to low and cook very gently for 4 minutes. Add the cilantro and toss gently. Serve hot.
Recipe courtesy of "Madhur Jaffrey's World Vegetarian", Clarkson Potter, 1999