Choose around a kg of the smallest chats (round washed new potatoes) you can find. You’re looking for the greatest surface area benefit, and parboil them. Set them aside and let them dry.
In a cooking pot, heat a healthy splurge of oil and when hot but not smoking, throw in a heaped tea spoon of black mustard seeds and cover them. When they have popped, add 2 teaspoons of turmeric and some very finely chopped green chilli to taste. Add the potatoes and swirl them around in the pot to coat them evenly with the spices. Grate a teaspoon sized piece of palm-sugar (jaggery) and squeeze the juice of lime and add both to the potatoes and give them another swirl.
Place them in an oven tray and bake them on relatively high heat to give a pleasant brown surface and wholly wonderful taste. Some people (that is people who have learned to like the taste) even sprinkle chopped fresh coriander over the chats in the serving dish.