In a microwave safe mug, first add the dry ingredients which are flour, cocoa powder, baking powder, sugar, instant coffee powder (if using) and mix with a fork.
Add milk, vegetable oil and whisk again with a fork till there are no lumps and the batter is smooth.
Sprinkle some white chocolate chips on top (if using).
Make sure that the batter is less than 1/2 the capacity of the mug.
If its more, the batter will overflow from the mug when the cake rises during cooking.
Place the mug on the turn table of the microwave and cook for 2 mins at micro high. (The high setting in mine is 900 W).
Let the mug rest in the microwave itself for at least 1/2 minute.
If you open the door immediately, the cake will deflate and sink in.
Wait for it cool down a bit and dig in.
Serve with some chocolate sauce drizzled on top or with a scoop of ice cream for a quick dessert.