I use two mugs, in one mug I place a very small amount of milk (between 0.5 and 1cm deep), I then fill the other mug with milk and place in the microwave on full for around 2 minutes. During this time I mix the cocoa powder and an artificial sweetener (don't like sugar in my cocoa) up into a thick paste in the small amount of milk. Once the microwave has done its thing I carefully remove the mug from it (with an oven mitt in case it has become superheated) and pour into the paste - mix for a few seconds and enjoy.