In a small saucepan, bring 100 milliliters / 3 1/2 ounces water to the boil, then add the tamarind and simmer for 20 minutes or until the water thickens, stirring occasionally. Remove from the heat an sieve the mixture into a bowl, set aside.
In a large saucepan, bring 500 milliliters / 1 pint water to the boil. Add the rice and a little salt to taste and cook for 20-25 minutes until the rice is tender. Drain and set aside.
Rinse out the saucepan and add the oil and place over a medium heat. Add the mustard seeds and, as they begin to pop, add the onion, peanuts, chana dhal or lentils, curry leaves, dried chillies and fenugreek seeds. Cook, stirring frequently, until the onions are soft and golden.
Add the asafoetida, chilli powder, coriander, turmeric and some salt. Cook over a medium heat, stirring, for 2-3 minutes. Pour in the tamarind water, mix well and cook for 15 minute or until thick.
Add the rice, stir to combine and remove the pan from the heat. Transfer the rice to a serving dish and garnish with the extra curry leaves.