First preheat the oven to 180 ° C (top / bottom heat). Meanwhile, put all the ingredients in a bowl in order, except for the cocoa, and stir well with a whisk.
After stirring, remove about 1/4 of the mixture and stir in the cocoa. Put the light mixture in a baking dish and smooth it out. Spread the cocoa mass on it.
Put the baking dish in the oven and bake the cake for 20 minutes.