How to make
Beat the eggs and sugar, until a white mixture is obtained. Gradually add the sifted flour mixed with the baking powder in portions, by alternating with water and oil and add the vanilla at the end.
Separate part of the mixture into a cup and mix it with the cocoa and part of the walnuts.
Pour half of the yellow mixture into a greased and floured cake tin, pour the brown mixture over it and mix it with a spoon.
Add the second half of the yellow mixture on top and place it in a preheated oven at 360°F (180°C), until it is nicely browned or until it's fully baked.
Melt the chocolate in a water bath and pour it over the already cooled and removed from the mold marble cake. Sprinkle the remaining walnuts.
The chocolate and walnut sponge cake is left to cool for a few hours.
NB: The mold of the cake should be deeper, because it swells a lot and fills the whole mold.
If desired, 2 tsp. of candied orange peels can be added to the sponge cake.