First we separate the egg whites from the yolks.
Mix the egg whites with the sugar, and mix the yolks with the oil (as for mayonnaise).
Add the yolks over the egg whites and lightly incorporate with a spatula.
Add flour, baking powder and essence and lightly incorporate with a spatula.
Divide the composition into 2 bowls, and add cocoa to one of them.
We put the compositions in 2 bags. We line the tray with baking paper and draw stripes from one end of the tray to the other with each color in turn.
Bake the cake in the preheated oven at 200 degrees for 20-25 minutes or until it passes the toothpick test. Powder it with powdered sugar as soon as we take it out of the oven, but let it cool before serving.