Took the recipe fr Agnes Chang.
I didn't use the exact filling recipe as I used the left over fillings for the wanton. So it the texture was flat and not springy.

Nevertheless this is the actual recipe:
Ingredients A: 350g minced meat, 200g shelled prawns, diced, 5 water chestnuts, chopped.
Seasoning: 1 ts salt, 1 ts chicken stock granules, 1 ts sesame oil, 1 tb sugar, 1/4 ts pepper, 1 1/2 tb starch powder
Ingredients B: 15 shiitake mushrooms, washed and soaked, squeezed dry.
Marinade: 1 tb soya sauce, 1 tb oyster sauce, 1 ts tapioca flour 1 tb oil
Method: Mix A with seasoning until mixture is sticky and springy. Mix B with marinade and season for 15 mins. Form mixture into 15 balls and cover with mushrooms. Steam with high heat for 15 mins until cooked. Serve hot.