Dice the pumpkin flesh, squeeze the lemons and rub the skin of 2 fruits (untreated).
Puree everything in the food processor and mix with the preserving sugar in a large saucepan. Cook over a high heat for about 3 minutes and make a gelation test. The jam can run a little longer, it thickens as it cools down.
Pour into twist-off glasses and turn upside down for 5 minutes.