Preheat the oven to 220˚C (425˚F). Put the potato on a chopping board, flat side down. Start from one end of the potato, cut almost all the way through, at about 3 to 4 mm intervals. Arrange the potatoes in a baking tray and insert the garlic in between the slits. Scatter some butter on top of each potato. Then drizzle the olive oil and sprinkle some sea salt and freshly ground black pepper. Bake the potatoes for about 40 minutes or until the potatoes turn crispy and the flesh is soft.