Dacher Keltner (or his lab at UC-Berkeley) did the original research. I can't find this one specifically, but their website is http://socrates.berkeley.edu/~keltner/

I managed to track it down with the search term 'leadership research "four cookies"' which led me to something with a reference to the study - http://www.yourofficecoach.com/YOCOfficeInsights/OI_bosses.h...