Separate the egg yolks from the whites. Half the powdered sugar mix until graying with the butter. Add the egg yolks one by one, then the flour, vanilla, lemon zest and baking powder. Mix well. Attention is one cup of the mixture and it is added cocoa. Pour the mixture into a buttered and floured previously rectangular baking dish and striped with the cocoa mixture. Bake until pale pink. The other half of the powdered sugar is mixed with the three egg white snow added the walnuts and 1 vanilla. With the obtained mixture is coated baked base, and again put in the oven to seal the top. Baked cake cut into small rectangles and add some icing sugar.