• Preheat your oven to 400°F (200°C).
• Roll out the puff pastry on a lightly floured surface to about ¼-inch thickness.
• Cut the pastry into three even rectangular sheets (about 4 x 8 inches). These will be the layers for your Millefeuille.
• Place the pastry rectangles on a baking sheet lined with parchment paper. Prick them with a fork to prevent them from puffing up too much during baking.
• Bake the pastry in the preheated oven for 15-20 minutes, or until golden brown and crisp. Once baked, remove the sheets from the oven and let them cool on a cooling rack.

2. Make the Pastry Cream:

While your puff pastry is baking and cooling, you can prepare the pastry cream:

• In a saucepan, heat the milk over medium heat until it’s just about to boil (small bubbles will form around the edges).
• In a separate bowl, whisk together the egg yolks, sugar, and cornstarch until smooth and pale.
• Gradually pour a small amount of the hot milk into the egg mixture while whisking constantly. This will temper the eggs and prevent them from curdling.
• Slowly pour the egg mixture back into the saucepan with the remaining milk and whisk constantly over medium heat. Continue cooking until the mixture thickens and comes to a boil, about 2-3 minutes.
• Once thickened, remove from the heat and whisk in the vanilla extract and butter. Continue stirring until the butter melts and the cream becomes smooth and glossy.
• Transfer the pastry cream to a clean bowl, cover it with plastic wrap (press the wrap directly onto the surface to prevent a skin from forming), and let it cool to room temperature. Once cool, refrigerate it until you’re ready to assemble.

3. Prepare the Icing:

To make the simple icing that tops your Millefeuille:

• In a small bowl, mix together the powdered sugar, water, and vanilla extract. Stir until smooth.
• If you want a decorative touch, melt dark chocolate in a microwave or over a double boiler. You can drizzle this chocolate over the icing for a beautiful contrast.