So yes, I did figure out what these things are. Jerusalem artichokes. I heard that every kilogram you plant into the ground yields about 50 kilos. What a nightmare. No wonder this friend gave us a big bag of it. Covered in mud, she said to throw it out if we didn't want to eat it. She suggested pickling it.
That's gross. So I decided to clean it up and serve it with some greens in a salad. Some were already turning mushy. But when they're fresh, they have this amazing crispy, crunchy texture. Pure white in colour too. I shaved off the skin and ran some through a mandolin, julienne-ing the others. With a really strong vinaigrette, it's not unpleasant. Earthy and not unlike ginseng. Health benefits are a bit dubious, but at least I learned something new. Now, what do I do with the other half bagful.