Thanks for the link, Glenn! That is an awesome set of cookers!
So, they started with a rocket stove in a sturdy base made of adobe bricks and cob:
Built this lovely complicated floor heating contraption, to heat the oven floor evenly:
Built a pretty standard cob oven on top:
And decorated it to make it gorgeous!
(They also attached a hot water system, to harvest excess heat from the oven - please, follow the link. There are many more pictures and more detail on what they did.)