Brush a sheet of the pastry with oil, then paint it with algae and charcoal powder to make a razor clam shell effect. Cut out twelve 10 × 2cm pieces and wrap each one halfway around a 15cm long tube mould to get a half-pipe shape. Wrap neatly in greaseproof paper and place on a baking tray. You need two of these per portion to create the faux shell, so make twelve.