Make the custard filling by heating the milk in a saucepan until just simmering.
In a separate bowl, whisk together the eggs, sugar and cornflour.
Slowly pour the hot milk into the egg mixture, whisking constantly.
Return the mixture to the saucepan and cook over medium heat, stirring constantly, until thickened.
Remove from heat and stir in the vanilla extract.
Allow to cool completely.
Preheat oven to 200°C (400°F).
Roll out the puff pastry and cut into two equal rectangles.
Place one rectangle on a baking tray and bake for 15-20 minutes until golden brown.
Allow to cool completely.
Spread the cooled custard over the baked pastry base.
Top with the second rectangle of pastry.
Refrigerate for at least 2 hours before serving.
