With a sharp knife, slice the potatoes taking care not to cut all the way through.
A great tip is to use two chopsticks on the sides of the potato which will prevent you slicing all the way through.
Place the potatoes in a large baking dish or roasting tray.
Melt the butter then add the chopped rosemary and garlic.
Season generously with salt and cracked black pepper and pour over the potatoes.
Place the potatoes in a preheated oven and allow to roast for 20-30 minutes (longer if using larger potatoes) until they are crisp, golden and tender throughout.