1. Prepare the Puff Pastry

Begin by preheating your oven to 350°F (175°C). Place each puff pastry sheet on a separate baking sheet. Bake for about 10 minutes or until each sheet turns a beautiful golden brown. Once done, remove them from the oven and set them aside to cool completely. This will form the base and top layer of your dessert.

2. Make the Vanilla Custard

Pour 3 cups of the milk into a large saucepan and heat it over medium heat until it just begins to boil. While the milk is heating, whisk the egg yolks and granulated sugar together in a large mixing bowl until the mixture is light and fluffy. Add the flour, vanilla extract, and the remaining 1 cup of milk to the egg mixture, stirring until smooth.

Once the milk reaches a gentle boil, gradually pour the egg yolk mixture into the saucepan, stirring continuously to prevent lumps. Continue to cook over medium heat, stirring constantly until the custard thickens, about 5-7 minutes. Once thickened, remove from heat and allow it to cool slightly.

3. Incorporate the Egg Whites

In a separate bowl, use an electric mixer to beat the egg whites until stiff peaks form. Gently fold the beaten egg whites into the warm custard mixture, being careful not to deflate the egg whites. This will give your custard a light, airy texture.

4. Assemble the Custard Layer

Take one of the cooled puff pastry sheets and place it at the bottom of a 9×13-inch baking dish. Pour the custard over the pastry, spreading it evenly across the dish. Place the dish in the refrigerator and allow the custard to cool and firm up for about 1-2 hours.

5. Prepare the Whipped Cream Topping

While the custard is chilling, whip the heavy cream with 2 tablespoons of powdered sugar until stiff peaks form. This should take about 3-4 minutes with an electric mixer. Once the custard has fully set, spread the whipped cream evenly over the custard layer.

6. Add the Final Puff Pastry Layer

Cut the second puff pastry sheet into 15 squares and carefully place these squares over the whipped cream layer, slightly overlapping if necessary. Return the dish to the refrigerator and chill for another 2 hours to allow the flavors to meld together.

7. Finish and Serve

Just before serving, dust the top with a light sprinkling of powdered sugar. This final touch adds an extra hint of sweetness and a beautiful finishing touch to your dessert. Serve the squares chilled for the best flavor and texture.