Boil the potatoes for 5 mins. Meanwhile, heat the oil in a frying pan and gently fry the onion for 8 mins. Add the garlic and spices, then fry for 2 mins more.
Drain the potatoes and tip into the onion mix. Turn up the heat and shake the potatoes around so that they are all covered. Cook for 10 mins more until tender, then serve with soured cream, sprinkled with a little cayenne.