Slice the potatoes to the thickness of your little finger, discarding the rounded end pieces. Tip into a pan of cold salted water and bring to the boil. Simmer for 3 mins until just cooked, then drain. This can be done a day ahead.
Rub each slice with a little oil and barbecue until golden and charred on each side.
Place in a dish and sprinkle with rosemary and garlic, if using.
Drizzle with a little more olive oil, season with salt and serve.
