That sauce does really taste exactly like the stuff that I always had in the japanese noodle restaurant close to my workplace! So here’s the (stolen and) “Farcyde-approved” 🙂 recipe:
60 g yellow rock sugar
150 ml soy sauce
300 ml Chinkiang black vinegar
150 ml red vinegar (optional, otherwise just use 450 ml Chinkiang)
Add rock sugar and soy sauce to a pot and heat on medium heat, stirring, until the sugar dissloves. You want a silky, sweet soy sauce syrup. Take off the heat, add the vinegar and fill into a storage bottle.
According to Mr. Liaw, this Dip can be “aged” in the refrigerator, always filling up the remnants of the last batch with new sauce.