Separate the yolks from the whites. Beat the yolks in a water bath, add half of the sugar. Beat the butter into foam and add the egg yolks to it, spoon by spoon. Mix the flour with the starch and sift the baking powder.
Add the sifted flour to the butter and egg yolks, while stirring constantly. Beat the egg whites into snow with the remaining sugar, and add them to the other mixture. To the resulting paste, add the ground walnuts, vanilla and stir until you get a uniform mixture. Pour the dough into a greased and dusted with flour baking dish.
Bake in a moderate oven for about 45 minutes. Once slightly cooled, take the cake layer out from the form and cut it into two layers using a thread.
To prepare the cream, melt the white chocolate in a water bath, add the milk and cocoa butter and whip. Begin to assemble the cake. Brush one of the layers with some of the white chocolate cream. Place the other layer on top and pour the remaining cream on. Decorate the cake with grated dark chocolate.