1) Preheat the oven to 180C/Gas 4. Spray a glass baking dish with cooking spray.
2) Place the olive oil, garlic, rosemary and salt and pepper, to taste, in a large resealable plastic bag. Add the potatoes, seal and toss to coat evenly.
3) Pour into the prepared baking dish. Roast the potatoes for about 30-40 minutes until crisp on the outside and tender on the inside.