Sayur Asam is one of my favourite menu. But, I think you should use galangal, not ginger. And one more thing, some Indonesian bay leaf would improve the taste, too. Happy cooking! :)
I really liked this soup. I made several changes. Used bagged walnuts in place of fresh peanuts (out of season), fresh Oregon pea pods in place of frozen green beans and omitted shrimp paste and shallot since I did not have any. After grinding walnuts, garlic, ginger, salt, and hot pepper in motar and pestle I took a taste and wow, it's very yummy and I could see this paste being used in other recipes. The sourness from tamarind contrasted very nicely with a bit of brown sugar - perfect. Thank you so much for introducing me this delicious soup tfirdaus.