Spread the olive oil in an oven proof dish. Peel and smash the garlic. Clean the potatoes and cut them into pieces about 2 inches wide. Spread the potato pieces in your dish and add the smashed garlic. Sprinkle the rosemary and salt and pepper according to your taste over the potatoes. Pour one and a half glasses of water into the dish. By adding water you make sure the potatoes cook evenly and you don’t need as much oil as without it. Bake the potatoes for 45 minutes at 200 degrees Celsius, until all the water is evaporated and the potatoes have formed delicious brown crusts.