Napoleonka (Polish mille-feuille)

Instructions

1. Preheat the oven to 200 °C (gas mark 7). Roll out the puff pastry and prick it with a fork.
2. Bake the pastry between two baking trays so it stays flat, for about 20 minutes until golden. Let it cool completely.
3. Heat the milk with the vanilla. In a bowl, whisk the yolks, sugar, flour and cornflour.
4. Pour the hot milk over the mixture while whisking, then return everything to the pan and thicken over low heat, stirring until it boils.
5. Off the heat, add the butter, cover with cling film touching the surface and let it cool completely.
6. Whip the very cold double cream with the icing sugar until firm, then gently fold it into the cooled custard.
7. Cut the pastry into two discs, spread the cream over one, then cover with the second. Chill for 2 hours before cutting.