1 Scrub the potatoes thoroughly and cook in boiling salted water for about 30 minutes, until fork-tender. Drain, peel and press through a potato ricer. Let the steam evaporate. Drain the quark and place in a bowl. Separate the eggs and mix the egg yolks, Parmesan and quark into the riced potatoes. Carefully fold the stiffly beaten egg whites in and season with salt, pepper and nutmeg. Let cool slightly.
2 Preheat the oven to 180°C (approximately 350°F). Grease a loaf pan.
3 For the filling: Peel the onion and cut into strips. Trim the leeks, rinse and chop. Rinse the cod, pat dry and chop. Beat the eggs with the cream and Parmesan then mix in the fish, olives, onions and leeks. Season with salt and pepper.
4 Spread the potato mixture over the base and sides of the loaf pan. Fill with the fish mixture, smooth the top and bake until golden brown, about 1 hour.