Combine the flour, melted butter, egg yolks, and warm milk and mix until you have a smooth dough that is a little stretchy.
Cover and leave to stand for half an hour or so
Cut a slit in each plum down one side and remove the stone
Combine the sugar and cinnamon in a small bowl and mix well
Fill each hinged plum with around ¾ tsp of cinnamon sugar
Put a large pot of water on the stove with 1 tsp salt and heat to boil
Work dough on a floured surface into a long sausage roll about 2.5cm in diameter
Cut the long roll into 3 equal rolls
Divide the first roll into 8 equal little pieces
Roll a small piece into a circle about 3mm thick and cup it in one hand
Take a hinged, filled plum and place it closed into the dough in your other hand
Gently smooth over the edge, rolling it around in your hand over and over until it is sealed and smooth
If it will not seal, use a dab of water, however generally I found it better to work with totally dry hands to accomplish the best results
Place the dumpling on a well-floured plate or back onto the floured surface
Depending on the size of the pot generally, 12 dumplings can be dropped carefully into the boiling water at a time
For the first 20 seconds ensure they are not sticking to the bottom of the pot or each other
They say they are ready when they float but I found they still need minimum 10 to 12 minutes
Remove with a slotted spoon and place into a colander
After draining for a minute you can put them on a plate and sprinkle cinnamon sugar on top or some may prefer to roll them in it to make them even sweeter.
At this point, they will no longer stick to anything except your tummy!
Recipe by Pantry Fun at https://pantryfun.com/plum-dumplings/