Cut potatoes into small pieces, put in a pot with cold water and bring to a boil.
Lower the temperature and cook them for 20-30 minutes.
When it is cooked, take it out of the water and mash.
Wait for it to cool down a bit, then add agave syrup, oat flour, semolina and corn starch and knead it until you get a soft dough. If it is still a bit sticky, add some more oat flour.
Separate the dough into 6 equal pieces.
Form each piece into a circle, put half of plum in the middle (you can add a small teaspoon of sugar if you prefer it sweeter) and carefully close it and form into a ball. Put it on a plate covered with flour.
Then put water in a wide pot and bring to a boil. When it's boiling put dumplings in water, lower the temperature and cook for 15 minutes (make sure it's boiling all the time).
When dumplings are cooked, put them on a plate, sprinkle with roasted semolina and oat flour and cinnamon.
You can also prepare some cooked plums on the side to dip dumplings in them.