Scrub the potatoes under cold running water and pat dry. In a roasting pan, combine potatoes, olive oil, salt and pepper. Using a large spoon or by shaking the pan from side to side, coat the potatoes evenly.
Roast the potatoes for 20 minutes. Sprinkle evenly with onion; drizzle evenly with chicken stock. Continue roasting 1 1/4 hours longer, shaking the pan every 10 to 15 minutes to rotate the potatoes, until they are brown and crusty and onions are caramelized.
Transfer to a serving bowl and garnish with parsley. Serve immediately.