Preheat oven to 200°C (180°C fan forced). Allow boiled potatoes to cool just enough to be handled

Lay potatoes out on a large baking paper covered tray. Using the flat side of a large chef's knife, smash potatoes (as shown in video)

Drizzle smashed potatoes with olive oil. Strip the rosemary and sprinkle over potatoes. Season with salt. Transfer to the oven for 30-35 minutes or until golden and crunchy. Season with extra salt and serve