I was on the way to work one morning and stopped into this Cambodian market along PCH, looking for bananas (I eat a lot of them with peanut butter!).
I used to drive all the way to Torrance to pick these up from one of the Japanese markets there. I was pretty shocked to find these here. The cashier/manager of the store was getting all stoked that >I< was stoked, then he went on to tell me they also carried Okinawan sweet potatoes as well.
I think they're also called Asian Sweet Potatoes as well.
Just wash, then dry thoroughly.
Poke the hell out of them with a fork.
Put in the oven. Maybe with tinfoil underneath it.
350 degrees for 1.5 to 2 hours, until the sugars start dribbling out the fork holes.