Begin by preheating your oven to 400°F (200°C). Roll out the puff pastry into a rectangular shape and cut it into equal-sized smaller rectangles. Place the pastry rectangles on a baking sheet and bake for 15-20 minutes or until golden and puffed. Meanwhile, whip the sterilized cream until stiff peaks form. Once the pastry rectangles are cool, layer them with vanilla pastry cream and whipped cream, creating a stack. In a separate bowl, mix premium cocoa powder with a bit of water to create a smooth chocolate drizzle. Decorate the top pastry layer with the cocoa drizzle and dust powdered sugar for an elegant finish. Your Napoleon Mille-feuille is now ready to be enjoyed, featuring layers of flaky puff pastry, creamy vanilla filling, and a touch of cocoa.