Making Napoleon Cake may seem daunting, but following these steps will help you create this delicious dessert with ease:

1. Preheat the Oven: Begin by preheating your oven to 400°F (200°C).

2. Prepare the Puff Pastry: Roll out the thawed puff pastry sheets on a lightly floured surface. Cut each sheet into equal rectangles, approximately 3×5 inches.

3. Bake the Pastry: Place the rectangles on a baking sheet lined with parchment paper. Prick the pastry with a fork to prevent it from puffing too much during baking. Bake for 15-20 minutes or until golden brown.

4. Prepare the Cream Filling: In a saucepan, combine milk, cornstarch, and sugar. Cook over medium heat, stirring constantly until it thickens. Remove from heat.

5. Mix Egg Yolks: In a bowl, whisk the egg yolks. Slowly add a bit of the hot milk mixture to temper the yolks, then gradually stir the yolk mixture back into the saucepan.

6. Finish the Cream: Return the saucepan to the heat and cook for another 2-3 minutes. Stir in the butter and vanilla extract, then let it cool.

7. Whip the Cream: In a separate bowl, whip the heavy cream until soft peaks form. Gently fold the whipped cream into the cooled custard mixture, creating a light and airy filling.

8. Assemble the Cake: Once the pastry layers are cooled, start stacking them. Place a pastry rectangle on a serving plate, spread a layer of cream filling on top, and repeat until all layers are stacked.

9. Chill the Cake: Refrigerate the assembled Napoleon Cake for at least 1 hour to allow the flavors to meld.

10. Serve: Before serving, dust the top with powdered sugar and garnish with fresh berries, if desired.

Following these steps will lead you to a delightful Napoleon Cake that will impress everyone at your gathering.