1Strain the fish broth through a fine-mesh sieve and discard the solids. You should have between 3 and 4 cups broth. Add water if necessary to bring it up to 4 cups. Pour the broth back into the pot, add the vinegar, and taste for salt.
3Meanwhile, place the bean threads in a bowl and add hot water to cover. Let soak for 15 to 20 minutes, then drain. Use scissors to cut them into shorter lengths if you wish. Set aside.
5Use a cleaver or sharp knife to finely chop the fish. Use the back of the cleaver or knife to pound on the chopped fish until they are completely mashed.
7Alternatively you can pulse in a food processor as well. I personally think it works better with food processor because it process the fish into a fine paste
8Place in a medium bowl, add the minced ginger, cornstarch, and salt, and use your chopsticks or fork to stir in one direction to blend everything. Wrap the bowl and leave it in the refrigerator for at least one hour.
10Lightly oil a plate. Wet both of your hands with water and scoop up about 1 Tbsp of the mixture and try to press it into a ball between your moistened palms. Set the ball on the plate. It will be a little bumpy perhaps, especially if you hand-chopped the fish; don’t worry. Repeat with the remaining fish mixture. You will have about 30-35 balls. Set aside.
12About 10 minutes before serving the soup, bring the broth to a rapid boil. Add the soaked bean threads and the fish balls and bring to a boil. Reduce the heat slightly and cook at a strong simmer for 5 to 7 minutes, or until the fish balls are cooked through; use a slotted spoon to turn the balls over so all sides are exposed to the hot broth. They will turn white and expand a little as they cook.
14Remove from the heat, add the sesame oil, and serve immediately. You can also individually serve this by allotting about 5 to 6 fish balls to each, as well as noodles, and broth, and top each with several leaves of coriander.
16Place the water in a medium pot, add the scallions, ginger, and fish heads and bones, and bring to a vigorous boil. Add the salt, partially cover, and cook at a strong boil for 20 minutes. Lower the heat, cover, and simmer for another half hour.