Whole garlic held warm and humid for weeks until the cloves turn black, soft and sweet — balsamic, molasses and tamarind, with almost no bite. It's browning, not fermentation, despite the name it's often given.
Delis and Korean grocers, as whole bulbs or peeled cloves. Or make it: a rice cooker on 'keep warm' for two to four weeks — in a shed, if you can, for the smell.
A little history
Developed as a health food in Korea and Japan, and in Western restaurant kitchens by the late 2000s.
Worth knowing
It isn't a swap for garlic. Mash it with a little oil or water into a paste and fold it into butter, aioli, glazes or a pan sauce for beef or mushrooms.