We have a yam that never made it onto a holiday table, but it has done much to nourish me. And it has done so without extra calories!The forgotten yam was in my pantry when I noticed it had begun to sprout. Normally, a sprouting tuber would go directly into the compost bin. This one was leafing out nicely, though, and I remembered how pretty yam vines can be. So I placed it on my windowsill, thinking that at some point I would plant it. It has been there ever since.It continues growing without any help from me. In its own …