Cut the potatoes into 1 cm dice. Heat the oil in a frying pan over a medium heat.
When hot put in the mustard seeds followed by the cumin seeds. Add the potatoes and stir a couple of times. Continue to cook for 15 minutes, stirring occasionally, until the potatoes are lightly browned and almost done.
Sprinkle in the ground coriander, cumin, cayenne and salt. Stir and cook for a further 1-2 minutes then serve.