The Napoleon is best eaten the same day. Martha made this recipe on episode 507 of Martha Bakes.
Preheat oven to 400 degrees. Roll out puff pastry on parchment to 11-by-15-inch rectangle. Sprinkle with sugar to evenly coat. Roll out again so sugar adheres to pastry. Trim to three 11-by-5-inch rectangles. Spray a rimmed baking sheet lightly with water and transfer pastry rectangles to baking sheet; freeze until firm, about 20 minutes. Divide rectangles between two parchment-lined rimmed baking sheets. Top each with a wire cooling rack and bake until beginning to turn golden, 25 to 30 minutes. Transfer to a wire rack to cool completely.
In a small bowl, whisk together heavy cream and espresso powder. Add confectioners' sugar and whisk until smooth. If glaze is too thick to pour, add additional cream, 1 teaspoon at a time, until glaze reaches a pourable consistency.
Assemble Napoleon: place one pastry rectangle on work surface. Top with half of pastry cream, spreading in an even layer. Top with a second pastry rectangle, pressing gently to adhere. Repeat with remaining pastry cream and pastry rectangle, with the flattest surface facing upward. Pour glaze on top and spread evenly using an offset spatula to cover. Fill a small pastry bag fitted with a very small plain tip (#1 or #2) with melted chocolate. Pipe lines of chocolate crosswise over the glaze, about 1/2 inch apart. Drag the tip of a wooden skewer down the length of the glazed pastry, in alternating directions, to create a decorative pattern. Refrigerate up to 1 hour before slicing with a serrated knife.