In a bowl, mix together the flour the sugar and the salt. Then add the eggs and mix.
Then, add the vanilla extract and the oil. If the batter is too hard to mix, you can pour a little bit of milk. Then add the milk gradually.
Pour some batter in an other bowl. Add the cocoa powder and mix. Cover the two bowl with plastic foil and put them in the fridge for 1 hour.
Heat a large pan, and apply a little bit of oil with a paper towel. Pour some chocolate batter, making drawings, then pour vanilla batter. Turn your pan so the batter is spread everywhere, then let it cook for 2 minutes.
Then turn it over, and cook for 1 minute. Then take it out of the heat. You can also begin by pouring some vanilla batter making drawings and cover with chocolate batter.