Recipe for the sesame dipping sauce for Beijing style Hotpot?

I tried asking this at the cooking community on Livejournal and was met with RESOUNDING silence, so I'm turning to Chowhounds for help. I've been craving huoguo for MONTHS now, and now that I've found a hotplate and a recipe for a Sichuan-style broth (in Fuschia Dunlop's Land of Plenty) I'm ready to make it. My problem is that I'm a northern-style huoguo loyalist and really want to be able to eat my hotpot with that amazing creamy sesame dipping sauce that you always get in restaurants in Beijing, but I can't seem to find a recipe for it. Does anyone know how to make this stuff, or if it can be bought premade? Thanks!