Do you believe these are purple yams? When I first saw them, I was doubtful, but lo and behold, after they're cooked, they look like this:
They are Japanese purple yams and are as sweet as candy. The first time I had purple yams was actually along a street in Hong Kong, but they were disappointing in flavor and not sweet at all. However, the ones I bought from the Chinese store are very sweet and yummy. Note that these are Japanese purple yams, not Japanese yams (which are ironically dark purple on the outside but yellow on the inside.)
