Roll the pastry out on a lightly floured surface and trim to a 30 × 19 cm (12 × 7½ inch) rectangle, then cut into 9 rectangles, each 10 × 6.5 cm (4 × 2½ inches). Transfer to an oiled baking sheet, leaving space between them, then chill for 15 minutes.
Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 10–12 minutes until well risen and golden. Transfer to a wire rack to cool.
Make the vanilla custard filling. Whisk the egg yolks and sugar together in a large bowl, then mix in the flours. Pour the cream and milk into a saucepan, bring to the boil, then gradually whisk into the yolks until smooth. Pour back into the saucepan and heat, whisking constantly, until thick. Beat in the vanilla extract, then take off the heat, cover the surface with a piece of crumpled and wetted baking paper and leave to cool.
Split each pastry in half through the centre. Sandwich 3 pastry halves together with the cooked custard and fruit. Repeat to make 6 pastry stacks. Dust with icing sugar.
Heat 3 metal skewers in a gas flame or under the grill until very hot. Press them into the icing sugar until the skewers form caramelized lines in the sugar. Repeat, warming the skewers between applications when needed.