Cook the potatoes in a saucepan of boiling water for 15 minutes or until tender. Drain and transfer to a large bowl.
Meanwhile, heat 1 teaspoon of the oil in a large nonstick frying pan over moderate heat. Add the onions and fry for 7 minutes or until golden brown and tender.
Add the sour cream, and a pinch each of salt, pepper and nutmeg, to the potatoes; mash well. Stir in the fried onions and shape into 8 cakes.
Heat 2 teaspoons of the oil in a 30 cm frying pan over moderate heat. Dredge the cakes in the flour, shaking off the excess. Fry 4 of the cakes for 3 minutes on each side or until golden brown and crusty. Repeat with the remaining oil and potato cakes. Serve with the yoghurt topped with chives.