This is such a simple dish that I never measure. Just eyeball everything according to your taste.
For the broth, put all ingredients in soup pot except for yu choy and scallion. Simmer for an hour and strain.
Once you've wrapped up your wontons, bring a pot of water to a boil. Drop wontons in. When they float to the surface and the prawn looks really pink, drain them and set aside.
To serve your soup, place some wontons in a bowl along with some blanched yu choy and scallion. Ladle in the boiling broth and serve.