1. Begin by making the crème pâtissière as it needs to chill in the refrigerator before being used. In a saucepan bring the milk and cream to the boil. Meanwhile, in a mixing bowl whisk together the egg, egg yolks, sugar and cornflour until thick and creamy. Pour over the boiling cream mixture and whisk for a few minutes. Return the custard to the pan and heat over a gentle heat, whisking all the time until the custard starts to thicken. Watch it carefully as it can easily turn into a scrambled egg-like mixture. Pass the custard through a fine-mesh sieve, scraping through with a spatula to get rid of any lumps. Leave to cool and then chill in the refrigerator. It is important that you cool the custard completely so that it is thick and not too runny. 2. Preheat the oven to 200°C (400°F) Gas 6. 3. Roll the pastry out thinly into a large rectangle, about 3mm thick. Cut the pastry into three long equal rectangles using a sharp knife, trimming the sides and ends to make them even. Place the pastry strips on the lined baking sheet. Brush the tops with a little milk and sprinkle lightly with caster sugar. Cover the pastry with another sheet of baking parchment and place a second baking sheet on top. 4. Bake in the preheated oven for 30-35 minutes until the pastry is crisp and golden brown. Check towards the end of cooking to ensure that the pastry does not burn. Once cooked, slide the pastry slices onto a cooling rack and leave to cool completely. 5. When you are ready to assemble, cut each pastry slice into six even slices, giving you a total of 18 pastry rectangles. Place six slices of pastry on a serving plate. Place the double cream, vanilla and icing sugar in a mixing bowl and whisk to stiff peaks. Spoon the thick cream into the piping bag and pipe small stars of cream around the edge of the six pastry slices, leaving a gap between each. Place a raspberry into each of the gaps. There should be a small cavity in the middle of the pastry and you should spoon or pipe a little of the cooled crème pâtissière into this. Place a small spoon of raspberry jam on top of the custard. 6. Place a second slice of pastry on top of each and then repeat the steps above, ending with a final pastry slice on top. Dust with icing sugar and chill in the refrigerator until ready to serve. They are best eaten on the day they are assembled (although you can prepare the pastry the day before), but will keep for two days stored in the refrigerator.