Preheat the oven to 200°C (400°F). Roll out the sheet of puff pastry and cut in two rectangular pieces. Cover with a thin layer of tapenade and mark the middle of the sheet with a little dent. Roll the pastry tightly from both sides to meet in the middle, looking like a cassette tape (remember?). Cut thin slices (about 7mm or ¼ inch) with a sharp knife and without squashing the double rolls too much. Place on a baking sheet covered in parchment and bake until golden brown, about 10 minutes. Leave to cool.