Prepare the Puff Pastry

1. Preheat Oven: Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper for easy cleanup.
2. Roll Out Puff Pastry: If using store-bought puff pastry, unfold the sheet and roll it out gently on a lightly floured surface. If it’s already thin, you can skip the rolling step.
3. Cut the Pastry: Cut the puff pastry into a rectangle, approximately 9×12 inches in size. You can cut smaller squares if you want individual servings.
4. Bake the Pastry: Place the puff pastry on the prepared baking sheet and bake for 12-15 minutes, or until golden brown and puffed up. Keep an eye on it, as puff pastry can burn quickly!
5. Cool: Once baked, remove the pastry from the oven and let it cool completely on a wire rack. This helps it maintain its crispiness.

Make the Vanilla Custard Filling

1. Heat the Milk: In a medium saucepan, heat the milk over medium heat until it’s warm, but not boiling.
2. Whisk Egg Yolks and Sugar: In a separate bowl, whisk together the egg yolks and sugar until the mixture is pale and smooth.
3. Add Cornstarch: Stir in the cornstarch to the egg yolk mixture, ensuring it’s fully incorporated and smooth.
4. Temper the Eggs: Slowly pour about half of the warm milk into the egg mixture, whisking constantly to avoid curdling the eggs.
5. Combine and Thicken: Gradually whisk the egg mixture back into the saucepan with the remaining warm milk. Cook over medium heat, stirring constantly, until the mixture thickens and comes to a gentle boil (about 5 minutes).
6. Add Vanilla and Butter: Once thickened, remove the custard from the heat. Stir in the vanilla extract and butter until fully melted and incorporated.
7. Cool the Custard: Pour the custard into a bowl, cover with plastic wrap (making sure it touches the surface of the custard to prevent a skin from forming), and allow it to cool completely.

Assemble the Puff Cake

1. Layer the Pastry: Once the puff pastry has cooled, carefully slice it in half horizontally, creating two layers.
2. Spread the Custard: Take one layer of the puff pastry and spread a generous amount of vanilla custard on top, smoothing it evenly with a spatula.
3. Top with Second Layer: Place the second layer of puff pastry on top of the custard, gently pressing down.
4. Chill: Refrigerate the assembled puff cake for about 30 minutes to allow it to set and firm up a bit.

Serve and Garnish

1. Dust with Powdered Sugar: Before serving, dust the top of the puff cake with a light sprinkle of powdered sugar for a sweet finishing touch.
2. Optional Garnishes: Add fresh berries or fruit on top to enhance the flavor and presentation. Strawberries, raspberries, or even a few mint leaves work beautifully.