Napoleonka Polish Custard Cream Cake

Instructions

1. Heat the oven to 400 F (200 C). Place each pastry sheet on a parchment-lined sheet pan, prick all over with a fork, cover with a second sheet of parchment and another pan to keep it flat.
2. Bake 20 to 25 minutes, until deep golden. Cool completely on racks.
3. Heat 600 ml of milk with the sugar and the vanilla seeds and pod until steaming.
4. Whisk the yolks, cornstarch, flour and remaining 150 ml cold milk until smooth.
5. Slowly whisk about a third of the hot milk into the yolks, then pour it all back into the pot.
6. Cook over medium heat, whisking constantly, until thick and bubbling, then 1 minute more so the custard reaches at least 160 F (71 C). Remove the pod and whisk in the butter.
7. Press plastic wrap on the surface and cool to room temperature.
8. Trim one pastry sheet to fit a 9 x 13 inch (23 x 33 cm) pan lined with parchment and place it in the pan. Spread the custard evenly.
9. Top with the second sheet, pressing gently. Chill 4 hours, dust with powdered sugar and cut with a serrated knife.