Russian Napoleon Cake with Crispy Puff Pastry Layers and Butter Cream

Napoleon cake starts with the flaky puff pastry. Cut the cold butter into small cubes and rub it into the sifted flour with your fingers or a pastry scraper until you get a rough crumble. Add the eggs, cold water, vinegar and salt. Quickly work into a smooth, non-sticky dough, overworking will cause the layers to lose their crispiness. Wrap in cling film and refrigerate for 1 hour.

Divide the dough into 10-12 equal portions. Roll each one directly on baking paper into a very thin sheet (about 24 cm in diameter). Prick all over with a fork to prevent puffing. Bake in an oven preheated to 200 °C for 5-7 minutes until golden. Leave to cool completely. Grind or crush one sheet into fine crumbs, these will be used to coat the finished cake.

In a saucepan, whisk the eggs with the sugar and flour until smooth, then gradually pour in the milk while stirring constantly. Cook over medium heat, stirring continuously, until the cream thickens and begins to gently bubble. Remove from the heat, add the vanilla sugar and leave to cool completely under cling film.

Beat the softened butter into the cooled cream a piece at a time, then whip with a hand mixer until smooth, glossy and fluffy.

Place the first sheet on a cake stand and spread a generous layer of cream over it. Continue with all the sheets. Coat the top and sides with the remaining cream and sprinkle with crumbs from the crushed sheet. Cover with cling film and refrigerate for at least 8 hours, ideally overnight.