Boil the potatoes in their jackets. Drain and cool them for 3–4 hours. Peel the potatoes and chop them into 2cm/¾ inch cubes.
Heat the oil in a 25–30cm/10–12 inch frying pan over a medium flame. (A non-stick or well-seasoned cast-iron frying pan would be ideal.) When the oil is very hot, put in the cumin seeds, mustard seeds and sesame seeds. As soon as the see