To make the layer, first beat 5 eggs with 1 cup sugar, add the flour with baking powder which you've sifted beforehand. Beat well and add 1 cup walnuts and vanilla. Pour the layer into a suitable oven dish, laid out with baking paper, and bake in a preheated 428°F (220 °C) oven. Cut the cooled layer into 2 separate ones.
Make a sugar syrup from 3 cups water, 1 cup sugar, 2-3 tbsp cocoa, 2 tbsp margarine or 1/2 packet butter by stirring them all in a pot on the stove until they come to a boil. Then add the rum (can substitute with cognac).
Start making the buttercream by beating 1/2 packet margarine with 3-4 tbsp sugar, 1 tbsp cocoa and then add 1-2 yolks, one at a time. Finally, flavor with 1 vanilla.
Syrup the cooled layers with the sugar syrup and smear with the buttercream. Sprinkle the smeared layers with caramelized sugar on top.
To make it, caramelize 1 cup sugar. Add 1 cup walnuts to it and distribute the mixture in a plate, which you've laid out with baking paper beforehand. Once the caramelized sugar cools, crumble it and sprinkle it over the cake layers. Stick them together. Smear the cake's top and sides with the buttercream and sprinkle on more caramelized sugar.
To finalize the cake, prepare the final cream mixture as follows. Caramelize 1 cup sugar again. Beat 3 egg whites to snow with 9 tbsp sugar (or less) and add the hot caramel to them in a thin trickle. Beat with a mixer while adding it and continue beating until it thickens well.
Use a pastry bag to distribute the final cream on top of the cake. If you have any caramelized sugar left over, sprinkle with it as well.