Preheat your oven to 170C.

Line a loaf pan with baking paper.

Separate the eggs in two different bowls.

Mix the egg yolks with the oil and vanilla and place aside.

Sift the flour with salt and baking powder.

Whip the egg whites until fluffy then gradually stir in the sugar until glossy and stiff, at least 5 minutes.

Using a spatula, fold in the egg yolks and oil then add the flour, spoon by spoon, folding it in gently.

Split the batter in half.

Mix the cocoa powder and water until smooth then stir it into half of the batter, adding the orange zest as well.

To finish the cake, layer the white batter with the black batter in your prepared pan: spoon one tablespoon of vanilla batter in the pan, top with a tablespoon of cocoa batter, followed by another spoon of white batter and so on until you run out of batter.

Bake for 40-45 minutes or until it passes the toothpick test.