Pre-heat the oven to 175 degrees.

Grease the tin well or use parchment paper or silicon mold.

Mix the oil, the sugar, the eggs, the milk and the baking powder together.

Divide the batter into two equal parts.

Put 175 g flour and the vanilla extract in a bowl, and stir together until well combined.

Mix the cacao powder and 120 g flour carefully into the other half.

Mix until you have a smooth mixture.

Pour alternatively the two mixture in a pan.

Bake for almost 50 minutes or until a toothpick inserted into the center comes out clean.