This was my try at answering a question on another thread and we really like how it turned out! Yum.
It is basically adding a creamy chocolate filling in the center of your mug cakes using nut butter and unsweetened cocoa powder.
Recipe and step by step photos
If you have other ways you do this that are no cheat, I'd love to try them too!!
My camera's battery decided to die here, so I didn't get as nice of a shot as I'd like, but you can see the outline of the filling in tact in the photo above.