In a bowl, mix together all the ingredients except the wonton skins. Fill and wrap the wonton skins (see step-by-step guide)
To make sure that the wontons don’t stick to the steamer rack, line the steamers with non-stick paper. I use baking paper and it does the trick really well. Make sure though that there is some space between the edges of the paper and the sides of the steamer so that the hot steam is not blocked by the paper lining.
Place only enough wontons in the steamer so that there is at least an inch of space between them. The wrappers will expand a bit during cooking and the wontons will flatten a bit so give them enough space to do that. If the wontons are too close together, their wrappers will stick to one another and it will be difficult to pry them apart without breaking the wonton skins.
Now, we begin steaming the wontons by placing the steamer in a pan of boiling water. The most common concern is how much water should there be in the pan. The level of water should be lower than the bottom of the steamer (i.e., the rack itself) so that the water does not touch the wontons.
If you have stackable steamers, arrange them one on top of the other. Note though that the wontons in the lowest rack will cook first. It is also important to remember to add more water to the pan as it evaporates during steaming.
After about 20 minutes in the steamer, the wonton skins would have lost their flour-y texture and they are now translucent and shiny.
Remember to take out of the pan first the lowest steamer rack. If you intend to serve the contents of all three racks at the same time, transfer the lowest rack on top to keep the wontons hot.
When the middle rack becomes the bottom rack, give it another ten minutes before moving it to the top, and so on.
Place the steamed wontons in a soup bowl, pour in enough broth, sprinkle with chopped onion leaves and cilantro, and serve the wonton soup hot.