Preheat oven to 220C (425F) and line a baking tray with baking paper.
Remove the rosemary leaves from the stem and (optional) using a pestle and mortar, grind the rosemary (which will release flavour and aroma). Add the olive oil to the rosemary and allow to infuse.
Wash, scrub and dry the potatoes.
Cut a thin layer off of the bottom of each potato, just enough so they don’t roll. Then cut slits across the potato, around 3-5mm (1/4-1/8th inch) apart, stopping just before you cut through so that the slices stay connected at the bottom of the potato. To make cutting easier, take two wooden spoons, or two chopsticks, and place them either side of the potato. This should prevent you from cutting all the way through.
Using a pastry brush, brush half of the infused oil evenly on all sides of the potatoes
Place the potatoes on the prepared baking tray and bake for 30 mins
Remove potatoes from the oven and carefully brush the potatoes with the remaining oil, making sure to brush oil right inside the potato slits. Sprinkle each potato with a generous pinch of salt (skip for babies / young children)
Return to the oven and bake for a further 30 mins or until the potatoes are crispy on the outside and cooked in the inside.