For the orange marmalade, peel the oranges and cut them into small pieces. Bring to the boil, then puree them with a hand blender or put them in a stand mixer and pass them through a blender.
Add the preserving sugar and bring to the boil. Let it simmer for 7-9 minutes, do a gelatinization test and fill into sterilized jars.
Turn upside down for 10 minutes, then let cool and store in a dark and cool place.