How to cook
Beat the eggs with the sugar, add the foamy yogurt with the soda in it and stir. Add the vanilla and sifted flour, and mix until smooth.
Divide the mixture into three equal-sized bowls, add the cocoa to one of them and stir.
In a baking tray lined with parchment paper and greased with a little fat, bake the 3 layers, one at a time, in a preheated 356°F (180-degree) oven. Remove the baked layers and place them on a wire rack to cool.
Meanwhile, prepare the egg custard, mix the milk and sugar in a metal saucepan and bring to a simmer. Separately beat the eggs, add a small amount of the milk and flour, and mix until smooth.
Add the mixture gradually, stirring constantly, to the milk and stir until it thickens. Remove the cream from the heat and add the butter, stir until completely melted and absorbed by the cream.
Assemble the cake, alternating: yellow layer - cream, brown layer - cream, yellow layer - cream, cover the cake on the side with cream, and decorate with little ground walnuts and a piece of grated chocolate.