Preheat the oven to 200C/400F/Gas 6.
Lay the pastry on a non-stick baking sheet. In a bowl, mix the egg white and icing sugar together, then spread over the top of the pastry. Transfer to the oven and bake for 15 minutes. Cut into four squares.
For the custard, whisk the egg yolks and sugar together in a bowl until pale and frothy.
Heat the milk with the vanilla pod in a pan until it reaches boiling point. Remove the vanilla pod. Pour the hot milk onto the eggs and whisk well. Pour the mixture into a clean pan and stir over a low heat until thickened.
To serve, place a slice of pastry onto a serving plate and pour over some custard. Layer up the remaining pastry slices and custard. Dust with icing sugar.