Making the Pastry Dough:

1. Prepare the butter mixture: In a large mixing bowl, combine flour, salt, and sugar. Add the cold cubed butter and use a pastry cutter or your fingertips to work it into the flour until the mixture resembles coarse breadcrumbs with pea-sized butter pieces remaining.
2. Combine wet ingredients: In a separate bowl, whisk together sour cream, eggs, and vodka (or vinegar) until well combined and smooth.
3. Form the dough: Pour the wet ingredients into the flour-butter mixture. Stir with a wooden spoon until the dough just comes together. It will look shaggy at first—that’s perfect! Turn it out onto a lightly floured surface and knead gently 3-4 times until it forms a cohesive ball. Don’t overwork it.
4. Divide and chill: Divide the dough into 8-10 equal portions (depending on how many layers you want). Shape each into a flat disk, wrap individually in plastic wrap, and refrigerate for at least 30 minutes or up to 2 days.

Baking the Pastry Layers:

5. Preheat oven: Heat your oven to 400°F (200°C). Line 2-3 baking sheets with parchment paper.
6. Roll out dough: Working with one dough disk at a time (keep others refrigerated), roll it out on a well-floured surface as thin as possible—aim for about 1/16-inch thickness or thinner. The thinner you roll, the crispier and more delicate your layers will be.
7. Cut circles: Using a 9-inch plate, pot lid, or cake pan as a template, cut out a perfect circle from the rolled dough. Prick the entire surface with a fork to prevent puffing. Transfer to a prepared baking sheet. Save all the dough scraps!
8. Bake: Bake for 5-7 minutes, until the pastry is golden brown and crispy. Watch carefully as thin pastry can burn quickly! The layers should be evenly golden and look dry.
9. Repeat: Continue rolling, cutting, and baking all remaining dough portions. You should end up with 8-10 crispy pastry circles. Bake the scraps too—these become your topping!
10. Cool completely: Let all pastry layers cool completely on wire racks. They’ll crisp up even more as they cool.

Making the Custard Cream:

11. Prepare egg mixture: In a medium bowl, whisk together egg yolks, cornstarch, and ¼ cup of the milk until smooth and no lumps remain. Set aside.
12. Heat milk: In a medium saucepan, combine the remaining milk, sugar, and salt. Heat over medium heat, stirring occasionally, until it just begins to simmer. Don’t let it boil.
13. Temper the eggs: Slowly pour about 1 cup of the hot milk into the egg yolk mixture while whisking constantly. This gradually raises the temperature of the eggs without scrambling them.
14. Cook the custard: Pour the tempered egg mixture back into the saucepan with the remaining milk. Cook over medium heat, whisking constantly, until the mixture thickens significantly—about 5-7 minutes. It should coat the back of a spoon and hold its shape when you draw a line through it with your finger.
15. Finish the custard: Remove from heat and immediately whisk in the butter and vanilla extract until completely smooth. For ultra-smooth custard, strain through a fine-mesh sieve into a clean bowl.
16. Cool: Press plastic wrap directly onto the surface of the custard to prevent a skin from forming. Let it cool to room temperature, about 30 minutes.

Assembling the Napoleon Cake:

17. Choose your base: Place your best-looking pastry layer on a serving plate or cake stand. If any layers cracked during baking, save those for the middle where they won’t be visible.
18. Spread custard: Spread about ½ cup of custard evenly over the pastry layer, leaving a small border around the edge. The custard will spread slightly as layers are added.
19. Stack and repeat: Place another pastry layer on top and spread with custard. Continue layering until you’ve used all pastry layers, ending with a pastry layer on top (no custard on the very top).
20. Crush the scraps: Place all the baked pastry scraps in a food processor and pulse until they form fine crumbs. Alternatively, crush them in a zip-top bag with a rolling pin.
21. Top the cake: Spread a very thin layer of custard on the top and sides of the cake. Generously press the pastry crumbs all over the top and sides of the cake, coating it completely. This is the signature Napoleon Cake look!
22. Chill overnight: Cover the cake loosely with plastic wrap and refrigerate for at least 8 hours or preferably overnight. This resting time is crucial—it allows the pastry to soften and meld with the custard, creating that perfect tender-yet-structured texture that makes Napoleon Cake so special.
23. Serve: Remove from refrigerator 15-20 minutes before serving to take the chill off. Slice with a sharp knife, wiping it clean between cuts for neat slices.