Add in eggs one by one and add in vanilla.

Pre-heat oven to 180°.Cream sugar and butter until fluffy.

Alternate flour and milk and be careful not to over whip.

Divide butter in another bowl and add the cocoa powder in one bowl.In your prepared tins alternate the batter to create a marble effect.Place in the oven for 1hr or until a toothpick inserted comes out dry.