1) Depending on their size and shape, halve, quarter, or leave the potatoes whole. 2) Heat the oil in a small frying pan until very hot, then add the ginger, garlic and chilli and stir-fry for a few seconds. 3) Pour over the potatoes and stir. 4) Dry-fry the cumin and mustard seeds in a small, heavy frying pan over a high heat until they give off a fragrant, nutty scent. 5) Crush using a pestle and mortar. 6) Add to the potatoes, along with the yoghurt, coriander and salt, and mix evenly. 7) Spoon into a serving dish and dust lightly with cayenne pepper.