Preheat the oven to 230C (210C fan assisted / 450F). Tip the potatoes into a large roasting tray and spread evenly.
Rub the rosemary leaves gently between your hands a few times to help release the flavour then tuck in amongst the potatoes. Break open the garlic bulb and put the cloves, lightly crushed but still with skins, in amongst the potatoes. Season plenty of freshly milled black pepper, and a little salt, if desired.
Bake for 30-40 minutes (according to pack instructions), then serve.