Anyway, WW got some sweet potatoes (Ipomoea batatas) and planted them.
It grows fast! It took about a week to get to this stage

but then, three days later it shot up!

There was another one (not photographed) that was in the kitchen - where there's plenty of light but not much direct sun, it grew considerably slower.
And today she planted it in the ground. It's classified as a vine, so I'm not sure if that means we have to watch out for it growing all over the fence?

Look at those leaves... thick and purplish. I'm not sure when to cut them off though, they are quite bushy and soon there'll be enough for a dish, I think...
Here are some recipes online:
Piggy's Cooking Journal (this one looks more like what you usually get in Malaysia)
Mental Masala