Then add the salt and oil. Mix everything well, divide up the mixture into 2 equal parts. Add the cocoa to 1 part. Prepare a slightly oiled tray.
Put 1 ladle of the white mixture in the middle. Right on top of it, pour 1 ladle of the cocoa mixture. Continue alternating between white and cocoa mixture until you've used them up.
Take a skewer and make lines from the middle of the cake out toward the edges (as if outlining the cake into the slices you're going to cut).
Then, on each slice, make lines from the edges going toward the middle. Bake in a preheated 338°F (170 °C) oven.