Preheat oven to 400 °F. Roll out the puff pastry until over 12-inches long. Brush a parchment lined baking sheet with oil. Place the puff pastry on top. Brush with water and sprinkle with half the sugar. Place another sheet of parchment on top followed by another baking sheet. Bake for 15 minutes. Remove from oven. Flip the pastry over and sprinkle with remaining sugar. Bake for an additional 5 minutes. Remove from oven and let cool. Slice into three even strips.
To assemble, cover the first layer of pastry with half the pastry cream (see our Here’s How instructions). Place another piece of pastry on top, followed by the remaining pastry cream. Place the last piece of pastry on top. Whisk together the icing sugar and cream. Frost the top of the pastry. Melt the chocolate in the microwave and place into a Ziploc bag with just the tip cut off. Pipe lines across the top.
To make a marbled pattern, run a toothpick down the center of the top lengthwise. Run the toothpick in the opposite direction halfway between both edges and the center. Chill until the frosting is set. Slice in pieces to serve.
Here's How: Pastry Cream
1. Split a vanilla bean lengthwise and scrape seeds. Heat 1 1/2 cups milk, vanilla bean and seeds over medium heat just until it starts to simmer.
2. In a bowl, whisk together 1/2 cup sugar and 1/4 cup cornstartch. Whisk in 4 egg yolks and continue whisking until light in colour.
3. Remove the vanilla bean from the milk. Slowly pour the hot milk into the eggs, whisking constantly. Pour the mixture back into the pot.
4. While whisking, cook the mixture over medium heat until it thickens and before it starts to boil. Remove from heat. Whisk in 2 tablespoons butter. Transfer pastry cream to a bowl and cover the surface with plastic wrap. Let cool then refrigerate at least 2 hours.