Par boil the potatoes whole in their skins for 20 minutes, drain and cut them into 1cm slices.
Heat the oil in a sauté pan. Lower the heat slightly and add the garlic, cumin seeds, onion granules, fenugreek seeds, mustard seeds and chilli flakes. Fry for 1 minute, then add the sliced onion and fry for 5 minutes until the onion are golden.
Add the potatoes and mix well, cover the pan with the lid and cook over a low heat, stirring occasionally for 15 - 20 minutes.