Toss the diced potato with the salt in a bowl. Set aside. Combine mustard seeds, fenugreek seeds and red chillies in a mortar and grind the spices, mixing them well. Mix with the tamarind extract and keep aside.

Heat oil in a shallow pan. Add curry leaves and asafoetida powder. Add salted potatoes and pan-fry them on medium heat till they turn a warm, golden colour. Add the tamarind extract with the spices and stir well. Continue to cook for 15-20 minutes.