make the pastry cream (creme patissiere)
In a medium pot, bring the milk and vanilla bean to a simmer over medium heat.
While the milk is heating, whisk the egg yolks and sugar together in a bowl until pale, slightly fluffy and smooth.
Add the cornstarch to the egg mixture and whisk well until combined and no clumps remain.
Pour the hot milk in a slow, thin stream into the egg mixture, whisking constantly. Return the mixture to the saucepan. Cook over medium heat, with constant whisking, until thickened and it comes to a boil. This will take about 2-3 minutes. Once the mixture comes to a boil, cook for about 1 minute more.
Remove the pastry cream from heat and add the butter. Stir until the butter has melted and fully incorporated into the pastry cream.
Transfer the finished pastry cream into a heat-proof bowl. Cover with a sheet of cling film, and make sure that the cling film is in direct contact with the surface of the pastry cream, this will help to prevent skin formation. Allow to cool completely to room temperature.
for the flaky pastry
Use an already rolled puff pastry sheet. Get the best quality you can (all butter preferred) Open and transfer dough to a lined baking sheet. Prick the surface with a fork to allow steam to escape. Place a second piece of baking paper on top of the dough. Set a second baking sheet on top, we want the pastry to stay thin and crunchy.
Bake for 20 minutes. Remove from oven and cool for 20 minutes on the pan, and then carefully lift it and place on a cooling rack to cool completely.
Once cooled cut into three same size rectangles using a serrated knife .
for the creme diplomat
Whip the cold cream on medium-high speed until medium peaks form, about 3 minutes. Add the chilled pastry cream to the bowl with the whipped cream. Beat on low speed until just combined and smooth. Do not over-mix. Chill.
to assemble
Fill a piping bag or a large plastic bag (and snip off a bottom corner with scissors) with the chilled diplomat cream. Starting with one of the pastry rectangles place one layer of puff pastry on a plate or platter. Pipe dots or a squiggly back and forth line of filling all over the pastry, then top with another layer of pastry. Repeat until there are three layers of pastry and three layers of filling, then arrange the raspberries on top.Refrigerate uncovered for at least 30 minutes before serving, dust with icing sugar before cutting. The soft filling will spill out the sides when you cut or bite into it, and that’s expected.
