Rinse the hawthorn, add to the pot with the water and Chinese plums. Bring to the boil
Reduce fire to medium (i use 5.5 on a Bosch induction stove which has a max of 9) so that the liquid is simmering. (You will see a few small bubbles.) Leave to simmer uncovered for 40 minutes.
At the 30 min mark, taste and see if the tartness is to your liking. If so, add the sugar and stir till dissolved. (If not, leave till 40 min and taste again. Repeat till you like the taste then add the sugar.) Note that if you're using rock sugar, it comes in clumps, so you may have to increase the fire to help it dissolve into the plum tea. Also, the flavour changes after chilling/ adding ice- to me, suan mei tang tastes tarter cold.
If drinking hot, sieve out the ingredientsportion out the tea then sprinkle some osmanthus flowers and add a new Chinese black plum to each cup (optional). If you prefer it cold, as I do, allow it to cool down with the ingredients steeping inside (this took me about 40 minutes) then sieve and pour the juice into a glass jar which goes into the fridge. As with the hot tea, add some osmanthus flowers and a fresh preserved plum to each cup before serving.
Store for no more than 2-3 days in the fridge. If you see it going cloudy, toss it.
Optional: you may want to freeze some of the plum tea juice in ice cube containers, so that you can use them to chill the plum tea. Using regular ice results in a diluted, watery drink
The sieved out ingredients can be used to make a 2nd batch of tea (see post for directions) or to make puree/ jam. They can also be eaten but they'll be mushy.