1 kg navel oranges
1 lemon
5 cups(1.1kg) Chelsea White Sugar

Wash and scrub oranges and lemon. Cut in half lengthwise then thinly slice. Place orange and lemon in a glass or ceramic bowl. Cover with 1 litre (4 cups) water. Cover bowl with plastic food wrap. Stand overnight.
Transfer orange mixture to a large heavy-based saucepan. Bring to the boil. Reduce heat to low; cover. Simmer for 1 hour or until zest is very soft. Add Chelsea White Sugar; cook and stir for 5 minutes or until sugar has dissolved. Increase heat to high. Bring to the boil.
Boil, uncovered, for 15 minutes or until marmalade gels when tested or reaches 105°C on a sugar thermometer. Stand for 5 minutes before pouring into hot sterilised jars; seal while hot.