Pre-heat oven 200C (400F/Gas Mark 6)
Peel and cut the potatoes into even sizes (aim for a size of a large egg, no smaller).
Par-boil the potatoes in boiling salted water for 10 minutes.
Drain the potatoes into a colander and vigorously shake to scuff the surfaces.
Leave to completely cool.
Pour a thin layer (1/4 cm) of oil onto a deep oven tray and heat in the oven until sizzling hot. Generously season the potatoes and add the hot oil. Turn (baste) the potatoes to ensure they are coated in oil.
Tuck the rosemary under the potatoes, and place the garlic halves cut side down into the tray.
Roast for 45 minutes or until the potatoes are golden and crisp, turning the potatoes again half way.