1. First of all, establish whether you have a dish large enough to fit the fish in but which will also fit into a steamer. I used an ordinary large serving plate that sat inside the wok – so I didn’t even need a rack underneath it. If you’re going to steam in a large pot, place a rack, a bamboo basket, an upturned bowl or something similar, to place your dish on. Best if the wok or pot has a lid – otherwise use another large plate or a board to cover it – wrapped in aluminium foil for snug fitting. Fill the pot or wok with water to an inch below the fish plate and set to boil.
2. Mix all the marinade ingredients together and let it steep for 15-30 minutes. Rinse the fish and pat it dry. Rub it generously with salt and pepper inside and out. Place it on the plate it’s going to steam on and pour the marinade over it. Let it stand for 30 minutes, turning once.
3. When the water’s boiling vigorously, set the plate with the marinade over the steam, cover tightly and steam for 12 minutes, then switch it off and rest for another 3 minutes while you prepare the spring onions. When done, the internal temperature of the fish should be 50C/120F and the flesh should flake easily off the bone.
4. Heat up the groundnut and sesame oil in a small pan until smoking. Add the spring onions and stir fry for a couple of minutes until charred. Dress the coriander sprigs with salt and sesame oil.
5. Carefully lift the fish plate out of the steamer, pouring out excess marinade. Top the fish with the spring onions, oil and all, and the coriander. If serving one fish between the two of you, lift the top fillet with two forks and divide between plates, remove the skeleton and dish out the bottom fillet in the same way.