Sieve together flour,baking powder,baking soda and salt and keep aside
In a bowl take sugar and beat in the eggs one by one.
Add oil and vanilla essence and mix well.
Fold in the flour lightly till Incorporated .
Divide this mix in two parts.
Add custard powder to one part and cocoa powder to another
In a greased pan,put the half of the custard cake mix lowermost.
Put half of the cocoa mix on top of it.
Similarly, put half of custard mix and cocoa mix on top.
Swirl the topmost cocoa mix with a spoon.
Bake in preheated oven at 180 degree Celsius for 25-30 minutes.
