Heat the oil in a large saucepan. Add the mustard seeds, dried chillies and curry leaves.
As the mustard seeds begin to pop, add the onions and stir-fry until lightly browned.
Stir in the coriander, garam masala, turmeric and chilli powder. Add the tomatoes and
cook for 5 minutes.
Meanwhile, peel the potatoes and cut into wedges or cubes, add them to the pan and cook
over a gentle heat for 5 minutes, stirring constantly. Pour in the coconut milk and an
equal amount of water. Cook for 15-20 minutes until the potatoes are tender. Serve hot.