Preheat your oven to 400°F (200°C). Roll out your puff pastry on a lightly floured surface to about 1/8 inch thick. Transfer it into a greased 9x9 inch baking dish and poke holes in the bottom to prevent puffing. Bake for 15-20 minutes or until golden brown.

In a mixing bowl, whisk together 2 cups of milk, 1 cup of sugar, and 1 tablespoon of vanilla extract until the sugar dissolves. Add in 4 large eggs and whisk until smooth.

Pour the custard mixture into a saucepan over medium heat. Stir constantly for about 10-12 minutes until it thickens and bubbles gently.

Remove from heat and let the custard cool for about 5 minutes. Whisk until smooth and glossy.

Once the puff pastry has cooled, pour the custard over it and spread evenly. Ensure it fills all corners.

In a mixing bowl, whip 1 cup of heavy cream until soft peaks form, about 3-4 minutes. Add 1-2 tablespoons of powdered sugar if desired, then spread over the custard layer.

Cover with plastic wrap and refrigerate for at least 4 hours or ideally overnight. Cut into squares and serve.