Choose small unripe walnuts, wash and pierce them in several places with a skewer. Soak them in cold water for 7 days, during which you need to change the water about 4 times – they blacken the water.
Then wash them well, put them in a pot with cold water and boil them. Pour out the water, boil again and repeat 2 more times (a total of 3-4 times).
Separately, boil a thick syrup of water, sugar and cinnamon. Once thickened to a jam density, leave to cool. Put the drained nuts in the cold syrup and bring to a boil. Remove the foam.
Remove from the heat and allow to stand for 1 night. The next day, boil on the stove once more until fully ready and add the citric acid at the very end.
Put the jam in dry and warm jars and close tightly.