Wash the oranges thoroughly. Quarter the fruit, remove pith and seeds and then slice thinly.
In a saucepan place the cut fruit, cover with water and bring to a boil. Strain and then return to pan.
Add the sugar, salt , one cup water and bring to a boil.
Reduce the heat to medium low and stew the fruit till the temperature reaches 220F or 103C on a candy thermometer 30 -35 minutes. Stir occasionally to make sure the fruit breaks down evenly.
Alternatively to check doneness for the marmalade take out a tsp and put in a frozen plate and see if it looks like it has a bounce. If yes then its done.
Take off the heat and add the Cointreau. Mix well cool and then fill in clean sterilized jars.
This marmalade keeps well in the fridge for up to a month.