1. Rinse and dry the fish thoroughly.
2. Wash the spring onions or baby leeks, cut off the roots, and remove the tops and outer skin if necessary. Split them lengthways, and lay half of them on an oval plate or dish large enough to take the fish and of a size to fit your steamer.
3. Peel and thinly slice the ginger and garlic, lay a few slices on top of the spring onions, and a few slices in the fish.
4. Put the fish in the dish, and sprinkle the remaining ginger and garlic on top. Cover with more spring onions. Pour over a tablespoon of soy sauce.
5. Place in a steamer and cook for 8 to 12 minutes.
6. Boil up the rest of the soy sauce and the sherry. Remove the fish from the steamer, uncover it, put the spring onions around. Pour the hot soy mixture over the fish and sprinkle on the sesame oil. Serve immediately.