1. Peel, rinse and mince water chestnuts.
2. Rinse and mince celery; Rinse and discard the stems of coriander.
3. Rinse spring onion; Mince the majority; Dice the remaining.
4. Whisk egg.
5. Rinse ground pork; Marinate in seasonings for 1 hour; Add minced water chestnuts, minced celery, minced spring onion and egg; Mix well by stirring in one direction; Slap the mixture hard to the cutting board for at least 10 times to be the filling.
6. Add some potato starch and some water in a bowl; Mix well to be the starch water.
7. Spray cold water on yanpi to soften; Cut into squares; Rub some starch water on the edges of each square; Wrap the filling to be yanpi dumplings; Arrange in a steamer with steamer paper; Steam over a high heat for 5 minutes; Remove.
8. Pour 4 cups of stock to a wok; Bring to the boil over a high heat; Add the yanpi dumplings and diced spring onion; Bring to the boil over a high heat again; Remove; Garnish with the coriander leaves. Ready to serve.
Yanpi dumplings is very popular is Fuzhou. Yanpi is made of pork and potato starch, which is available in Chinese grocery stores.