First and foremost, ignore the coffee mix in the pictures. I was making coffee to go with my brownie! (It was delicious together by the way!)
Now add some water to make it a thick runny texture! If you've made brownies before, you'll know what your consistency preference is. Stir, stir, stir well!
Be sure to be careful when you get the mug out of the microwave. It will be very hot! I advise to let it cool for a few minutes before indulging! :) Enjoy!