Napoleon Cake

Steps

1. 1
   Heat the oven to 200°C. Divide the puff pastry into 6 equal pieces and roll each on baking paper into a 24 cm square or round, about 3 mm thick.
2. 2
   Prick each sheet all over with a fork so it rises evenly instead of ballooning, and chill for 10 minutes.
3. 3
   Bake one or two sheets at a time for 12–15 minutes, until deep golden and crisp right through — pale pastry turns soggy under the cream. Trim each sheet to an even shape while hot, keep the trimmings and cool everything on a rack.
4. 4
   For the cream, whisk the eggs, sugar and cornflour with 200 ml of the cold milk until smooth. Heat the rest of the milk until steaming.
5. 5
   Pour the hot milk into the egg mixture while whisking, return it to the pan and cook over medium heat, whisking constantly, until it boils and thickens; let it bubble for 1 minute.
6. 6
   Take off the heat, whisk in the vanilla, press cling film onto the surface and cool to room temperature.
7. 7
   Beat the soft butter until pale, then beat in the cooled custard a spoonful at a time to a smooth, fluffy cream; the butter and custard must be at the same temperature or the cream splits.
8. 8
   Stack the sheets on a serving plate, spreading cream generously between them and over the top and sides.
9. 9
   Crush the trimmings into fine crumbs and press them all over the cake.
10. 10
    Cover and refrigerate for at least 8 hours, ideally overnight, until the pastry has softened and the cake cuts cleanly.