Boil the potatoes whole in their skins in salted boiling water. Drain and skin.
Heat up the oil in a frying pan/wok. Add the onions.
Add black mustard seeds/cumin/garam masala/garlic to the oil. Make sure nothing burns.
Stir in the potatoes, the lemon juice, the coriander. Continue to fry gently together until fragrant.
Remove from the heat and when cool enough to handle, make tiny chickpea sized balls of potato. Set aside.