•  5 eggs. The yolks and whites are separated
• 200 g sugar, or less if you want it less sweet.
• 4 tablespoons of vegetable oil
• Some vanilla extract or vanilla sugar
• 200 g flour
• 1 teaspoon of baking powder
• 2 tablespoons of coco powder
• A pinch of salt
• Optional: grated zest of an orange or lemon

Tip: Sift the flour to make it airier.
Important: Make sure you have all the ingredients ready and that the oven is on before you start. You want to waste as little time as possible while mixing to prevent the batter from losing fluffiness.

Preheat the oven at 175-180°C. You want the oven ready when the batter is done to prevent the batter from losing fluffiness.

Separate the egg whites from the yolks and put them in two separate bowls. Beat the eggs using a mixer. As they mix add the sugar a little at the time. Mix until the sugar has melted into the egg whites and foam becomes stiff like a  meringue. You want it stiff enough so it still stays put in the bowl when turned upside down. Add the oil, vanilla sugar and lemon zest into the bowl with the egg yolks and mix them lightly. Then use a scraper (or something similar) to carefully fold the egg mix in with the meringue foam. You want to add a little at a time.

Mix the baking powder and salt into the flower and fold the dry ingredients into the meringue batter a little at the time. Use wide, circular motions, bring the spatula all the way to the bottom to incorporate the flour well throughout the batter incorporate the flour and not destroy the fluffiness of the batter at the same time. It is better to lose some of that fluffiness than to have those flour bubbles. The batter should feel much thicker at this point.
In a separate cup mix the coco powder with a few tablespoons of water to make a cream. Pour half of the batter into another bowl. Add the coco cream with the same fold in motion as before.

Grease up a bread tin with butter then coat the buttered tin with a little bit of flour. Make sure it covers everything, also the sides.
Pour in the light batter and then the coco batter on top. Use the scraper to lightly mix the two batters to create a marbling effect. You can experiment with different sorts of motions to get different patterns.

Bake it in the middle of the oven at 180°C for 30-40 minutes. The cooking time depends on the size of your tray. Keep an eye on the cake after 20 min. If it starts getting golden on top then you can test to see if it is done by sticking it in the middle with a wooden skewer ( or a chopstick or a toothpick). It is done if you remove the stick and there is no batter on it. If after 35 min the inside is still not done but the top looks quite brown and cooked, try turning the heat down a bit, and you can also cover the tray with some aluminum foil (it doesn’t have to be a tight cover, just loosely over the tray to hopefully speed the cooking inside. Remove the cake from the oven when the inside is done, and let it cool down before cutting it. After it’s cool, you can also powder the top with some powdered sugar for serving.