According to the omniscient Wikipedia, fermented tofu is made by allowing cubes of dried tofu to fully air-dry under hay and slowly ferment from aerial bacteria and fungal spores. Lovely.
Fermented tofu is sometimes referred to as Chinese cheese. It's pretty pungent stuff - it does smell a bit fruity, like a well-aged blue cheese. I have known others to eat it straight from the jar, which I have considered in the name of blog-testing, but... well... I can't. It just doesn't smell too good. In a recent episode of the F Word, Gordon Ramsey described it as a Chinese delicacy and blind-folded James Corden for him to eat raw. I didn't particularly agree that it was a delicacy (it's obtained quite easily and cheaply) but I did feel sorry for him.
However, when used to cook vegetables in, particularly stir-frying water spinach and other leafy greens, it's completely transformed.The basic base to stir-frying vegetables with this fermented tofu lies in ginger, garlic and chilli. I finely dice equal amounts, and fry it in a little oil. Add one or two cubes of the fermented tofu and mash a little. Add the vegetables, maybe a splash of water or rice wine and stir-fry until cooked.
The fermented tofu makes the vegetables very fragrant, and your kitchen a little stinky, so keep your windows open. I like the smell of it frying but then again, I also like the smell of shrimp paste frying.
There is also fermented red beancurd which is mainly used in braising meats, as far as I can tell. I haven't used it... yet!