Time-lapse video of the process, narrated by me, from start to finish - I first record the screen while painting, over a period of several weeks.
Then I edit in Camtasia, speeding it up, some parts 10x faster. This makes the whole video about 20 minutes long in most cases. Finally I add a voice-over explaining everything I'm doing step by step, sometimes going off on tangents about related subjects. :)
You also get the final high-res psd file, with all layers intact.