Heat the oil in a kadhai. Add the urad and chana dals. When the urad dal begins to change colour, add the mustard and asafoetida. When the mustard splutters, add the curry leaves and the potato pieces.
Add the turmeric powder, chilli powder and salt. Mix well. Cover and cook for 5-7 minutes. Remove the lid and mix the potatoes. Simmer for 10 minutes, tossing the potatoes every 2-3 minutes till the potatoes are nicely browned. This is a great accompaniment to rice with sambar, rasam, dal... in short, a great accompaniment to anything.