Australian Vanilla Slice

Preheat your oven to 400°F (200°C).
Roll out the sheet of puff pastry and cut it in half. Place the two halves on a baking sheet lined with parchment paper and prick them all over with a fork.
Bake the puff pastry for 15-20 minutes, until golden brown and crispy. Remove from the oven and let it cool.
In a medium saucepan, combine the milk, egg yolks, granulated sugar, cornstarch, and vanilla extract. Whisk everything together until smooth.
Heat the saucepan over medium heat, whisking constantly, until the mixture thickens and comes to a boil. Continue to cook for 1-2 minutes, until the mixture is very thick.
Remove the saucepan from the heat and transfer the mixture to a bowl. Cover the surface with plastic wrap to prevent a skin from forming and let it cool to room temperature.
Once the puff pastry and pastry cream are both cool, spread a thick layer of the pastry cream over one of the puff pastry halves. Place the other half of puff pastry on top of the cream layer.
Use a sharp knife to cut the vanilla slice into 8 equal portions.
Dust the tops of the vanilla slices with powdered sugar before serving.