When the water comes to the boil, turn down the heat and sink the dumplings in.
At first, they will go to the bottom, then rise to the surface. If they stick to the bottom of the pot, shake it lightly or peel them off carefully with a spatula.
Let simmer for 10-15 minutes, depending on how well cooked you want the plums to be. You can leave them for 5 minutes, but the plums will be a little raw.
I boiled the dumplings in two batches, nine at a time, in a five liter pot.