Beat margarine and sugar till light and fluffy. Add 1 egg at a time beating in between to form peaks. Add vanilla essence.
Sieve flour and baking powder in a separate bowl.
Add 3 tbsp of flour mixture to the butter at a time while continuing to mix till ur done with all the flour.
Scoop three tablespoon from vanilla cake batter put in a bowl, add tablespoon tablespoon cocoa and a tablespoon of milk and mix it. Then pour half of vanilla cake batter in a greased tray then pour chocolate batter