Caramel for Pastry Cream
In a covered pot over high heat, bring 1 cup sugar, corn syrup and 1/4 cup water to a boil. Remove lid and let sugar boil, brushing sides of the pot with water intermittently, until sugar turns an amber colour, about 10 minutes. Remove pot from heat and whisk in whipping cream, watching out for steam that rises when cream is added. Set caramel aside.
In pot over medium heat, bring milk and vanilla extract to a simmer.
In a bowl, whisk together egg yolks, sugar, cornstarch and salt. Whisking egg mixture constantly, gradually add milk, one ladle at a time to the egg mixture until all the milk has been added.
Pour mixture back in pot and return to medium heat. Whisking vigorously, bring mixture up to a simmer. Due to the cornstarch, pastry cream will thicken quickly, about
Pour pastry cream into a bowl and whisk in caramel. Cover surface of pastry cream with plastic wrap and cool completely, about 3 hours. Pastry cream can be prepared up to 2 days in advance.
Preheat oven to 375 F.
On a lightly floured surface, roll out puff pastry to 1/4 -inch thickness. Cut 18 discs
3 inches in diameter and place on a parchment-lined baking sheet. Chill discs for
20 minutes. Before baking, dock pastry with a fork.
Place a sheet of parchment on top of discs and place a second baking sheet on top of parchment, to weigh the discs down. If your baking sheets are rather light, place additional weights on the baking sheet (ie a few ramekins or a glass baking dish).
Bake for 20 minutes. Remove the top pan and sheet of parchment. Brush discs with egg wash and return to oven for anther 8-10 minutes, until golden brown in colour. Allow to cool.
Place all ingredients except vanilla in a pot and simmer over medium heat for 5 minutes, stirring occasionally until thickened.
Remove from heat and stir in vanilla.
Chill until ready to serve.
Place one disc on a plate (or on a tray). Using a large star piping tip or a large spoon, pipe or dollop caramel pastry cream onto the disc. Place another disc on top and repeat process. Top third disc with a dot of pastry cream. Dust napoleons with icing sugar and serve with butterscotch sauce.