1. Preheat oven to 400 degrees. On a lightly floured surface, roll out puff pastry to a 10-by-15-inch rectangle. Transfer to a baking sheet lined with parchment paper.

2. Prick pastry all over with a fork. Cover completely with another sheet of parchment paper; weight with another baking sheet (same size or slightly smaller) to prevent pastry from puffing up unevenly. Bake, occasionally pressing top sheet down, until pastry is golden, 30 to 40 minutes. Remove top sheet and parchment, and let pastry cool.

3. Transfer pastry to a cutting board. With a serrated knife, carefully trim and discard edges; cut into 12 equal pieces.

4. Dividing evenly, put a large dollop of pudding (2 to 3 tablespoons) on 8 of the 12 pastry pieces; top with raspberries and a little more pudding.

5. Assemble napoleons on serving plates: For each napoleon, stack two pieces of pastry already topped with pudding and raspberries, then top with a plain piece. Dust lightly with confectioners' sugar.

6. Make Raspberry Sauce (optional): In a small bowl, stir together 1/4 cup raspberry jam and 1 tablespoon water; pass through a fine-mesh sieve. Thin with additional water if needed.

7. Garnish plate with Raspberry Sauce, if desired.