I believe I've found it. I also read that many restaurants also add rice vinegar to the recipe for this sauce. It's called Nuoc Cham dipping sauce and you can either make it yourself by looking up the recipe or you can find it on Amazon...
Hey there!
This post is so Very late I know... BUT!! I am also from Michigan! I lived there for over 40 years. I have been searching like crazy for the recipe for this sauce too! All the common recipes that result from the searches are: ALL sauces found
are definitely too thick, not 'tart'...