Peel pumpkin seeds and peels. Cut into small cubes.
Sprinkle the pumpkin with sugar and mix gently.
Dissolve the sugar over low heat. Then increase the heat and bring to a boil. Leave the jam to infuse overnight.
Bring the pumpkin to a boil, add cinnamon if desired and remove from heat. At this point, the pumpkin will become transparent. Let the jam cool for a bit, then put it on the fire again, when the pumpkin begins to acquire an amber color, add citric acid.
Put the finished jam in sterile jars and roll it up.