Preparing eel isn't difficult, but it can be unpleasant because of the slippery, slimy skin. Most seafood vendors will offer to remove the skin for you, but for this dish, you need it on (it's delicious to eat). To remove the slime, you just salt the eel thoroughly, then rinse it off.
Chinese black beans have been salted, fermented and dried. Chun pei is dried, aged tangerine peel; you will need one piece from a whole tangerine. These ingredients are sold in the Chinese section of supermarkets.
Sprinkle salt liberally over the eel and rub it into the skin. Leave it for 30 minutes, then use the back of a knife to scrape the skin to remove the slime. If the eel still feels slippery, repeat the salting and scraping process.
Rinse the eel then dry it with paper towels. Trim off and discard the fins. Cut the eel into cross sections about 2cm thick and place them in one layer, cut side up, in a wide, shallow, heat-proof bowl.
While the eel is salting, briefly rinse the black beans and chun pei under cool running water, then put them in separate bowls. Add just enough warm water to cover the black beans. Add a sufficient amount of warm water to the bowl with the chun pei, so the peel can "swim" freely. Leave for about 20 minutes, or until soft.
Cut the chun pei and ginger into very thin matchsticks. Drain the black beans and chop them roughly. Thinly slice the garlic and cut the chillies into thin rounds, squeezing out and discarding the seeds as you go. Scatter these ingredients over the eel.
Stir the soy sauce with the rice wine and sugar, and pour this over and around the eel.
Place the dish on a tiered steamer (or on a low rack in a wok) set over boiling water. Cover with the lid and steam for 10 minutes, or until the eel is cooked through.
While the eel is steaming, slice the spring onions into fine julienne. Heat the oil in a small pan until very hot.
Remove the eel from the steamer and top with the spring onion and coriander. Pour the oil over the aromatics to wilt them, then serve immediately with steamed rice and stir-fried green vegetables. Take care when eating the eel because it has fine, soft bones.