Roll out the puff pastry on a lightly floured surface to a 3mm thickness. Cut the pastry into 4 rectangles about 11 x 7cm and prick them all over with a fork, then lay them on a baking tray. With the point of a knife, mark a line all the way round the rectangles about 3mm from the edge. Brush the edges with beaten egg, and leave to rest in the fridge for 1 hour.
Cut the top 10cm of the