Heat the oil in a pan over a medium heat. Fry the mustard seeds, curry leaves and asafoetida until they begin to crackle, then add the onions. Cook for 3-4 mins until the onions are slightly golden.

Stir in the tomato purée along with the diluted sambar masala. Tip in the potatoes, 1 1/4 tsp of salt and mix well. Lightly crush the potatoes with a wooden spoon and cook for a further 3-4 mins. Taste for seasoning. Serve garnished with the coriander.