In a medium saucepan, heat the milk over medium heat until it just starts to simmer.

While the milk is heating, in a separate bowl, whisk together the egg yolks, sugar, and cornstarch until smooth and pale.

Once the milk is hot, slowly pour it into the egg mixture, whisking constantly to temper the eggs and prevent them from curdling.

Return the mixture to the saucepan. Add the vanilla bean seeds (or vanilla extract) and cook on medium-low heat, whisking continuously, until it thickens to a creamy custard consistency.

Remove from heat, cover with plastic wrap directly on the custard's surface to avoid a skin forming, and allow it to cool completely.

In a mixing bowl, whip the heavy cream until soft peaks form.

After the custard has reached a cool temperature, carefully combine it with the whipped cream, folding it in delicately to achieve a smooth and homogenous mixture.

Set aside.

Preheat your oven to 400°F (200°C).

Roll out the puff pastry on a lightly floured surface to smooth it out.

Cut it into two equal rectangles to match the shape you want for the final custard slices.

Place the puff pastry sheets on a baking sheet lined with parchment paper and prick them all over with a fork to prevent excessive puffing.

Bake in the preheated oven for about 15-20 minutes, or until golden and crisp.

Place one sheet of puff pastry on a serving tray and spread an even layer of vanilla custard cream over it.

Gently place the second sheet of puff pastry on top of the custard layer, pressing down slightly to ensure it adheres.

Dust the top with powdered sugar, if desired.

Transfer the assembled dessert to the fridge to chill for at least 1 hour, allowing the custard to set.

Once ready to serve, slice into squares with a sharp knife. Enjoy!