Chop pork into large chunks measuring 2x3x4 cm, season for 15 minutes with fish sauce. Then mince for 3 minutes using a food processor. This is called giò sống (pork paste).
Soak mushrooms in water so that they expand. Remove the stems and cut the larger mushrooms into smaller pieces.
Dice green onion and coriander.
Cooking:
Bring 1 liter of water to a boil and add salt.
Roll pork paste into small balls (5 g/ball) and add to boiling water, then add mushrooms. When the soup returns to a boil and the pork balls float, sprinkle it with green onion and coriander.
Ladle into 2 large bowls and sprinkle with pepper. Serve hot.