Mix the yellow of the egg-yolk with the lemon rind and 200 gr of sugar.
Then add the oil and the milk and follow mixing until getting a homogeneous batter.
In a bowl sieve the flour with the baking-powder and add it to the batter.
At the end mix the egg white until foamy, add then little by little the sugar and finally blend this with the other batter.
In a rectangular baking shape with parchment paper add the batter and bake this on a pre-heated oven at 170 °C for around 50 min.
(or until when trying with a toothpick it comes clean out.)
When it coolsdown cut it in blocks and cover them with confectioner's sugar and the Nutella.