The mystery vegetable was pretty tasty. Thanks everyone for your ideas! The kids said, "Good, but not as good as artichokes." They are fans of artichokes. Maybe because of being allowed to make a big mess of the table with all the leaves. Or being able to dip in lemon butter sauce. Or because I only buy them when they are on sale. The flavor of cardoon was somewhat similar to artichokes.

I made cardoon gratinee, with cream sauce, parmesan and lemon zest. And everyone said they'd eat it again.