1 For the pastry, thaw puff pastry the day before. Then overlap the sheets and roll out to a 40 x 25 cm rectangle (approximately 16 x 10 inches). Cut the sheets into two rectangles each 20 x 25 cm (approximately 8 x 10 inches). Transfer to a parchment-lined baking sheets. Stir together sugar and cinnamon and sprinkle over the dough. Let rest 30 minutes.
2 Bake in preheated oven at 220°C (gas mark 4-5, fan: 200 degrees) (approximately 425°F) for about 15 minutes. Let cool on a wire rack.
3 Soak gelatin sheets in a bowl of cold water until softened, about 10 minutes. Stir together sugar with sherry until the sugar has dissolved. Stir in the gelatin and refrigerate.
4 When the liquid begins to gel, whip the cream with the vanilla sugar and fold into the sherry-gelatin mixture. Transfer to a piping bag with a large plain piping tip.
5 Put a puff pastry on a serving plate and top with half the whipped cream. Place the second layer of puff pastry. Shape small dollops of cream on the top layer of puff pastry. Refrigerate for 1 to 2 hours. Dust with cinnamon before serving.