Dry roast whole dry red chillies, urad dal and black peppercorns. Cool and pound to a coarse powder.
Heat oil in a kadai. Add mustard seeds, curry leaves, small onions and sauté till lightly browned. Add potatoes, stir and add salt.
Cover and cook till the potatoes are almost done. Add the masala powder and mix. Cover and cook over low heat for about three to four minutes or till the potatoes are done.