Preheat the oven to 200°C, fan 180°C, gas 6. Taking each potato, cut slits across with a small knife, 3mm apart and no more than two thirds down (use a pair of chopsticks on the chopping board either side of the potato and at right angles to the knife to stop it from cutting all the way through). When all the potatoes are done, nestle them together in a roasting tray.
Drizzle the potatoes with olive oil, rolling to coat, then arrange with the cut sides up. Add a bay leaf to each potato, season with freshly ground black pepper and transfer to the oven.
Bake for 50 minutes until crispy and golden on top.