First in a mixing bowl add powdered sugar, oil and mix/whisk till creamy.
Now add vanilla essence and mix well.

Now sieve maida, baking powder and baking in the bowl and mix well.

Now add milk (little at a time) and mix by cut and fold method.

Now devide the mixture into 2 separate bowl equally and add cocoa powder in one portion and give it a good mix.(U can also add chocolate essence if u have)

Now in microwave safe mug first pour tbsp of batter of vanilla mixture and then add tbsp of mixture of chocolate batter. repeat this process till it fill half.

Keep mug in microwave for 1 min and check by inserting toothpick after done.
(keep 30 sec for more if needed, it depends the size of the mug).

Delicious Chocolate vanilla mug cake is ready.