Remove scales and rub some salt (about 1 tsp) all over the fish and rinse with water. Pat dry with paper towel. Now rub cornstarch all over, and place into a heat-proof steaming dish. Cover with cling wrap and set aside.

Wash Chinese coriander, and cut a 4-cm (2-inch) length from the stalk end, keeping the roots. In a small saucepan set over medium heat, bring water to a boil. Add coriander head and roots, and boil for about 15 minutes. Discard coriander, add rock sugar and continue to simmer until rock sugar dissolves. Add light soy sauce, dark soy sauce, and chicken stock granules (powder), and stir to combine well. Taste (it should be just slightly salty with a hint of sweetness). Add more sugar if too salty, or more water if sauce thickens. Bring back to boil for a minute, then turn off heat, and set aside.

In a small saucepan, heat up oil over medium heat. When oil is just hot, put in chopped garlic. Keep stirring to fry evenly, until garlic just starts to turn golden brown (do not over-cook, otherwise the garlic will become bitter-tasting) . At this point, immediately sieve out the garlic and drain on paper towel, leaving oil in the saucepan. Now put in the sliced ginger strips, and stir-fry in the oil until it turns golden brown at the edges. Sieve out from the oil, leaving the oil in the saucepan for later.

Prepare the steamer. When water comes to a rapid boil, steam fish over high heat for 12 to 15 minutes (depending on the size of your fish). Test for doneness with a fork. If the flesh easily flakes off, fish is done.

Meanwhile, shred spring onion, and soak in water until it curls up (about 1 - 2 minutes). Drain and set aside.

When fish is done, drain the juices from the dish. Place fried garlic, ginger strips and shredded spring onion on top. Heat the garlic-ginger oil in the saucepan until very hot. Drizzle 2 - 3 tbsp of oil over the fish, followed by 2 - 3 tbsp (or to taste) of special soy sauce. Serve immediately.