Grease a microwave safe bowl and keep it aside. Grease it all over, on the base as well on the sides. Grease it really well othewise the cake may stick to the bowl while inverting. It is better if you use a glass dish only, as plastic is not good for heating purposes.
Take all the dry ingredients- flour, baking powder, baking soda, salt, coffee powder and sugar in a bowl.Whisk properly using a wire whisk so that everything gets mixed nicely. Alternatively, you can sift the dry ingredients.
Make a well in the centre, add oil, vanilla essence, yogurt and milk. (See Note 10)
Mix everything with light hands preferably using cut and fold method. Do not beat it vigorously otherwise the batter will develop gluten and the cake will turn out to be chewy.
Keep the batter thick only, ribbon-like consistency.
Lastly, add vinegar and mix it well.
Tap it to release air bubbles if any. Take care that you tap it with some towel or cloth if you are using a glass dish.
Pop it in the microwave for 5 minutes. (See Note 11)
Insert a toothpick in the centre of the cake to check for the doneness of the cake. (See Note 11)
Take the bowl out and let the cake cool completely. (See Note 12)Once completely cool, invert it in a plate.
Spread Chocolate Ganache on the cake.Decorate with silver balls or sprinkles or gems.