Preheat oven at 180°
Mix curd and sugar till sugar dissolves
Add baking powder and baking soda and mix it
Add maida and mix it in cut and fold method
Add vanilla essence and oil in it
Divide the mixture in two portion
In one part add cocoa powder and mix it
In a grease mould put one spoon white batter than pour one spoon cocoa batter on its centre
Repeat this portion till batter finished
With help of knife make a patter on it
Bake it in oven at 180° for 25 minutes or till toothpick inserted comes out clear
Cool it on wire rack and cut in pieces