Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.

Unfold the thawed puff pastry sheet on a lightly floured surface. Gently roll it out into a slightly larger square, about 1/8 inch thick.

Using a sharp knife or pizza cutter, cut the pastry into even squares. Aim for a size that pleases you, but keep in mind that larger squares will require more custard and whipped cream per layer.

Carefully transfer the pastry squares to the prepared baking sheet, leaving a little space between them for puffing.

Using a fork, gently prick the center of each pastry square a few times. This helps prevent them from puffing up too much in the middle.

Bake the pastry squares for 20-25 minutes, or until golden brown and puffed. Remove them from the oven and let them cool completely on a wire rack.

In a medium saucepan, whisk together the milk, sugar, and cornstarch until smooth.

Heat the mixture over medium heat, whisking constantly, until it thickens and begins to bubble.

In a small bowl, whisk together the egg yolks. Slowly whisk the hot milk mixture into the egg yolks to temper them. Be sure to whisk constantly to avoid curdling the eggs.

Once combined, return the mixture to the saucepan and cook over medium heat, whisking constantly, for another 1-2 minutes until the custard thickens significantly. The custard should coat the back of a spoon.

Remove the custard from the heat and stir in the vanilla extract. Pour the custard into a bowl or container and press plastic wrap directly onto the surface to prevent a skin from forming. Let the custard cool completely at room temperature, then refrigerate for at least 1 hour.

In a chilled bowl, use an electric mixer to whip the heavy cream until stiff peaks form. Be careful not to over-whip, as the cream can become clumpy.

Once the custard is chilled and the pastry squares are cool, it's time to assemble!

Place a pastry square on a plate. Spread a generous amount of the chilled custard over the top, leaving a small border around the edge.

Dollop a heaping spoonful of whipped cream onto the custard layer.

Gently place another pastry square on top, creating a sandwich. Repeat this process with the remaining pastry squares, custard, and whipped cream.

Dust the top layer of your assembled squares with powdered sugar for a touch of sweetness and elegance.

You can also get creative with other toppings! Drizzle with melted chocolate, arrange fresh berries on top, or sprinkle with chopped nuts.