Preheat your oven according to your preferred settings for pastry.

Unroll the thawed puff pastry sheets on a clean surface and cut them into even rectangles.

Place them on a baking sheet lined with parchment paper, ensuring the pastry pieces do not overlap.

Bake the prepared puff pastry sheets in the oven until they are puffed up and golden brown.

Keep an eye on it toward the final minutes of baking to ensure it doesn’t overcook.

In a saucepan, combine the whole milk and granulated sugar over medium heat, stirring occasionally.

In a separate bowl, whisk the egg yolks and cornstarch together until smooth.

Gradually pour a small amount of the warm milk mixture into the egg yolk mixture while whisking continuously.

Once you have tempered the egg yolks, pour the mixture back into the saucepan with the remaining milk.

Continue to cook over medium heat, stirring constantly until the custard thickens and bubbles gently.

Remove from heat and stir in the vanilla extract, then let the custard cool slightly.

Once the puff pastry has cooled slightly, slice each piece horizontally.

Spoon the cooled vanilla custard generously onto the bottom halves of the puff pastry.

Replace the tops and gently press to secure them in place.

Dust the tops with powdered sugar just before serving.

Slice into pieces and serve at room temperature or slightly chilled.