2) Roll the puff pastry out into a 30cm by 37cm rectangle. Spread the pesto evenly over the pastry, to within 0.25cm of the edges. Fold the dough in half lengthwise over the pesto.
3) Roll the dough out again into a 30cm by 37cm rectangle. If any of the pesto squeezes out, scoop it up and spread it over the top of the pastry. Sprinkle the Parmesan over the new rectangle.
4) Cut the dough crosswise into 1cm thick strips. Twist each strip into a corkscrew. Arrange the twists on the baking tray and press down the ends to prevent them unrolling. Bake for 10 minutes, until puffed up and golden brown.