Preheat oven to 220°C Spray a shallow baking dish with olive oil.
Cut a thin slice from the bottom of each potato. Place cut side down on a work surface. Lay a wooden spoon parallel to potato. With base of knife resting on spoon handle, thinly slice each potato without cutting all the way through.
Place potatoes in prepared dish. Fan slices. Brush with 1TB of butter. Sprinkle with pepper. Bake for 1 hour.
To prepare desired topping, combine ingredients in a bowl. Mix well. Sprinkle over potatoes. Drizzle with the remaining butter. Bake for 15 minutes. serve immediately.