Boil the potatoes in a large pan of salted water until they are just done (don’t let them cook so they fall apart or they will be difficult to handle later).

In the meantime heat the oil in a large pan over a medium heat and fry the whole spices for 15 seconds. Add the onion and continue to fry gently until light brown. Don’t let the onion or the spices burn. Add the turmeric and chilli powder, stir and fry for 30 seconds. Add the cooked potatoes and the chopped tomatoes and salt seasoning. Stir to coat the potatoes with the spice mixture. Allow the mixture to cool for 5 minutes then stir in the yogurt before serving.