Step 1

In a medium saucepan, combine milk and vanilla bean and seeds. Bring to a simmer over medium heat.

Step 2

In a large bowl, whisk cornstarch, sugar, egg yolks and salt. Whisk in cream.

Step 3

Remove vanilla bean from hot milk. Gradually add milk to the egg mixture, whisking constantly, until thoroughly incorporated. Transfer the mixture back to the saucepan and whisk constantly over medium heat until it almost comes to a boil and is thick enough to coat the back of a spoon, 3-4 minutes. Remove from heat and whisk in butter until smooth.

Step 4

Transfer the pastry cream to a heatproof bowl and cover with plastic wrap, pressing the plastic directly onto the surface. Refrigerate until cold, about 2 hours or up to 3 days.

Step 5

On a piece of parchment paper, stack the two separate pieces of thawed puff pastry. Roll them out to one 12X12-inch square, trimming to make even sides.

Step 6

Cut the square into three 4X12 inch strips and transfer the strips to a parchment lined baking sheet, spacing apart.

Step 7

Prick the dough all over with a fork and chill until firm, 30 minutes. Meanwhile, preheat the oven to 425F

Step 8

Transfer the baking sheet to the preheated oven. Bake the pastry sheets for 10 minutes, until golden around the edges.

Step 9

Set another baking sheet directly on top of the pastry strips and continue to bake for 8 minutes more.

Step 10

Remove the top baking sheet and continue to bake until the pastry is golden brown 6-8 minutes more. Cool completely.

Step 11

In a medium bowl, whisk the confectioner's sugar, corn syrup, butter and enough of the milk to reach a consistency that is pourable but still thick. Transfer ¼ of the glaze to a small bowl and whisk in the cocoa powder.

Step 12

Transfer the chocolate glaze to a piping bag fitted with a ⅛-inch tip.

Step 13

Pour the white glaze onto one of the pastry strips, spreading it evenly with an offset spatula.  Pipe lines of the chocolate glaze horizontally across the white glaze, about ½-inch apart.  Drag the tip of a toothpick down the length of the glazed strip in alternating directions to create a pattern. This is called "feathering." Let set 10 minutes.

Step 14

Fit a pastry bag with a ½-inch round tip and fill it with half of the pastry cream.  Pipe an even layer of the pastry cream onto one of the remaining pastry strips.  Fill the pastry bag with the remaining pastry cream and pipe evenly onto the remaining strip.  Transfer these two pieces to a serving platter or plate, stacking on top of each other.

Step 15

Place the glazed piece of puff pastry on top of the pastry cream.  Slice with a serrated knife and serve.