I had this warming Karen version of sour soup in a village not far from Moulmein, the port at the mouth of the Salween River. Rather than being fish-broth-based, as many sour soups are, it is made with pork and freshly cooked greens. The shrimp paste (ngapi) is very subtle and blends into the other flavors seamlessly.
Serve as a main dish over rice, perhaps with some roasted root vegetables or a crisp salad on the side. Leftovers are exceptionally good the next day.