1 package (about 17 oz) of puff pastry (preferably store-bought for convenience)
For the pastry cream:
2 cups whole milk
1/2 cup granulated sugar
1 vanilla bean (or 1 tablespoon vanilla extract)
6 large egg yolks
1/4 cup cornstarch
1/4 teaspoon salt
2 tablespoons unsalted butter
For the icing:
1 cup powdered sugar
1/2 teaspoon vanilla extract
2 tablespoons milk
For assembly:
Confectioner's sugar (for dusting)
Instructions:
Prepare the Puff Pastry: Preheat your oven to 400°F (200°C). Roll out the puff pastry on a floured surface to about 1/8-inch thickness. Cut the pastry into 3 equal-sized rectangles and place them on a baking sheet. Prick the pastry all over with a fork to prevent puffing, then bake for 12-15 minutes or until golden brown. Allow to cool completely.
Make the Pastry Cream: In a saucepan, heat the milk and vanilla (scraping seeds from the vanilla bean if using) over medium heat until simmering. In a separate bowl, whisk together the egg yolks, sugar, cornstarch, and salt. Slowly pour the hot milk into the egg mixture while whisking constantly. Return the mixture to the saucepan and cook, whisking constantly, until it thickens (about 5 minutes). Remove from heat and stir in the butter. Pour the cream into a bowl, cover with plastic wrap, and let it cool completely.
Make the Icing: In a small bowl, mix together the powdered sugar, vanilla extract, and milk to create a smooth icing. You may need to adjust the amount of milk to achieve the desired consistency (thicker for drizzling).
Assemble the Mille Feuille: Once the puff pastry and pastry cream have cooled, place one pastry layer on a serving dish. Spread a generous layer of pastry cream on top. Add the second pastry layer and repeat with more pastry cream. Top with the third pastry layer. Using a spoon, drizzle the icing over the top layer in a zigzag pattern. Dust with powdered sugar.
Serve: Allow the Mille Feuille to chill in the refrigerator for about 30 minutes before serving. Slice into portions and enjoy!