Wash oranges and lemon hot and dab dry. Peel the peel in zests. Peel oranges in such a way that the white skin is also removed. Use a sharp knife to remove the orange fillets between the parting skins, catching the juice.
Squeeze separating skins with your hand.
Squeeze the lemon. Place the lemon with the citrus peel, orange fillets and juice (total approx. 600 g) in a large pot. Mix in jam sugar. Bring to the boil while stirring. Boil for about 4 minutes while stirring until bubbly, then possibly make a gelling test.
Pour into hot rinsed twist-off glasses. Close the jars and place them on the lid for about 5 minutes. Turn them over and let them cool down.