This is a fairly common caudiciform plant, Cyphostemma juttae. It makes a nice fat base, and gets green leaves in summer, then goes dormant for winter.
I don't remember where I got this one, either, unfortunately. This one died shortly after we moved to TN. It started to grow a little arm out of the side of it, and I think I got excited and overwatered it. Had it in quite a lot of shade, too, which probably didn't help.