Place peeled and cubed potatos in large bowl, with diced onion,rosemary, salt/ pepper and olive oil. Meanwhile in oven roast garlic cloves in a piece of aluminum foil with a drizzle of olive oil and salt & pepper, secure foil and roast in oven 30-40 minutes til softened,remove from foil, remove garlic skin and smash with fork then add to bowl of potatos, mix all ingredients well and cover and let sit in fridge for about an hour.
Remove potatos onto baking sheet, cook in 375 degree oven for abt. an hour or until golden. Move the potatos around and gently turn them to ensure even browning,abt every 10 min or so.