Peel and cut the potatoes into small cubes. Heat oil in a large frying pan. Add the urad dal, cumin seeds, mustard seeds, and dry red chillies. When seeds splutter, add the curry leaves. Fry for 30 seconds.
Add the potatoes and salt. Stir fry till potatoes till they are cooked, about 20 minutes. Add red chilli powder and cumin powder. Fry for another 2 – 3 minutes. Serve hot with plain rice.
Note: Another nice variation is to add 1 coarsely chopped onion and some sliced garlic cloves alongwith the potatoes.