Preheat the oven to 400 F (200C).
Place the potatoes in a large saucepan, and add water to cover. Bring to a boil, and once the water comes to a boil, boil potatoes for 2 minutes. Drain the potatoes, and gently pat dry with paper towels.
Pour the oil into a roasting pan or deep oven tray. Place in the oven to heat for a few minutes. Once hot, add the potato cubes and a big pinch of salt and pepper, and toss to coat the potatoes well in the oil. Make sure they are in a single layer. Return the tray to the oven and roast for 15 minutes.
Mix together the rosemary and garlic, and once potatoes have roasted for 15 minutes, add the rosemary and garlic, and toss to combine. Return potatoes to the oven and roast for another 15-20 minutes until golden brown and cooked through. If you want to, you can broil for the last 1-2 minutes to get an even deeper color.
Remove from the oven and enjoy hot!