Sift flour, cocca powder, baking powder, baking soda twice.
In a deep bowl, mix sugar powder, oil, egg yolks and water and slowly mix to blend together till smooth. This can get tricky, don't be too hard and over mix here.
Beat egg whites, sugar and salt till soft peaks are formed.
Blend the egg white meringue into egg yolk mixture slowly making sure not to loose the volume.
Fold the dry mixture and mix to form a smooth batter.
Pour into a 12"x15" tray which has been greased and lined with butter paper, let the batter be only 1/4" high maximum.
Bake 180C for about 5-6 mins till done. Remember not to over do it as it will loose the spongyness and softness and will become very dry.
Let it cool completely and using a butter paper, roll and let it set for about 2 hours.
Open the roll now and spread a layer of truffle cream on top of the cake.
Spread the whipped cream and walnuts in a very thin layer on top of the truffle cream of make alternate rows to see the design in the final roll as I did. (seen in the picture below)
Roll again and then let it set for 2 hours. And then cut into slices and enjoy!