Ingredients:

  Amount  Measure       Ingredient -- Preparation Method
--------  ------------  --------------------------------
   3      medium        boiling potatoes -- scrubbed
   2      tablespoons   vegetable oil
   1      teaspoon      black mustard seeds
   1      teaspoon      cumin seed
   3      tablespoons   onion -- finely chopped
   1                    green chile -- finely chopped or
   1                    red chiles -- finely chopped
   1      tablespoon    fresh coriander -- finely chopped
     1/2  teaspoon      salt
   1      cup           plain yogurt

Preparation:

Drop the potatoes into enough boiling water to cover them completely and boil briskly, uncovered, until they are tender but still show some resistance when pierced with the point of a small, sharp knife. Drain the potatoes in a colander, peel and cut them into 1/2 inch cubes. In a heavy 8-inch skillet, heat the vegetable oil over hight heat until it starts to smoke. Stir in the mustard and cumin seeds and, when they crackle and begin the burst, immediately add the onions. Stirring constantly, add the chili, coriander and potatoes. Cook over moderate heat, turning the potatoes frequently with a spoon, until the cubes are well coated with the spice mixture. Remove the skillet from the heat and stir in the salt. Place the yoghurt in a small serving bowl, add the entire contents of the skillet, and toss gently together. Taste for seasoning, cover tightly, and refrigerate for at least 1 hour, or until completely chilled.