Preheat air fryer to 400 degrees for 5 minutes. 2. Clean and dry the potatoes, and cut them in half. Transfer cut potatoes to a medium mixing bowl. 3. Toss potatoes with the rosemary, salt, pepper, olive oil, and melted butter until well coated. 4. Transfer potatoes to the preheated air fryer. 5. Cook at 400 degrees for 25 minutes, flipping, stirring or shaking the basket halfway through to ensure even browning. 6. Transfer to a serving platter, and top with a bit more coarse salt, and fresh chopped rosemary.