• Preheat oven to 425°F.
• Line a baking sheet with parchment paper; set aside.
• On a well-floured countertop, stack both pieces of thawed puff pastry on top of each other. Roll into a 12”x12” square. Cut into three equal 4”x12” rectangles. Prick the dough every 2 inches with a fork.
• Lay the rectangles onto the prepared baking sheet. Place a sheet of parchment paper on top of the rectangles. Next, place a second baking sheet directly on top of parchment paper. Set a large oven-safe dish on top of this second baking sheet in order to weigh it down. (Note: This step ensures that the pastry rectangles bake flat and do not puff up too much in the oven.)
• Bake rectangles at 425°F for 10 minutes.
• Remove the dish, extra baking sheet and top piece of parchment paper. Return the rectangles to the oven and bake for 6-8 more minutes, or until golden brown. Set baked rectangles aside to cool. (Note: The sheets will puff up in this last stage, but they will deflate again once baked.)

For the Pastry Cream

• In a medium bowl, whisk together the egg yolks, sugar and cornstarch until smooth and pale in color. Set aside.
• Using a medium saucepan, heat the milk over medium heat until it just begins to simmer. (Tip: Stir milk often to prevent it from scorching.)
• Slowly pour half of the hot milk into the egg yolk mixture, whisking vigorously the entire time. Pour this egg mixture back into the saucepan with the remaining milk. (Tip: Use a fine mesh strainer when you pour the egg mixture back into the saucepan. This will ensure a smooth pastry cream later.)
• Bring mixture to a boil over medium heat and then continue cooking for 1 more minute, stirring constantly the entire time. Remove mixture from the heat, and add the the butter and vanilla extract; stir until fully combined and smooth. Set pastry cream aside to cool. (Note: The pastry cream will thicken quickly at this stage. It becomes somewhat difficult to stir, but keep stirring to prevent the cream from burning!)

For the Icing

• In a medium bowl, whisk together the powdered sugar, milk, vanilla and melted butter until smooth. (Note: The consistency of the icing should be thick but still pourable. If necessary, add a small amount of additional powdered sugar or milk to create a thicker or thinner icing as needed.)
• Pour approximately ¼ of the icing into a separate small bowl. Whisk the cocoa powder into this portion to create the chocolate icing. (Tip: You may need to add a splash of milk to the chocolate version.)

To Assemble

• Place one pastry rectangle on a large plate or cutting board. Spread half of the pastry cream on top.
• Place a second pastry rectangle on top; press gently into the pastry cream. Spread the remaining pastry cream on top.
• Place last pastry rectangle on top. Using an offset spatula, spread the vanilla icing evenly across top.
• Transfer the chocolate icing into a pastry bag fitted with a small round tip. (Note: You can also use a sandwich bag with a tiny corner snipped off.)
• Pipe 4 straight lines of chocolate icing lengthwise down the rectangle.
• While the icing is still wet, drag a toothpick back and forth horizontally across the rectangle to create the traditional Napoleon decoration. (Note: For each line, alternate the direction that you drag the toothpick.)
• Refrigerate for 1 hour. Using a serrated knife, trim the edges of the Napoleon.
• Slice remaining rectangle into smaller pieces before serving.