Lightly dust a 30 x 45 cm (12 x 18 inch) baking tray with flour. Roll out the pastry on a lightly floured surface to a rectangle the approximate size of the baking tray. The pastry should be rolled out as thinly as possible—thin enough to read through. Carefully lift the pastry onto the baking tray cover with plastic wrap and refrigerate for 20 minutes.