Place the oranges in a large saucepan and cover with water. Bring to the boil and cook for 1 hour, until soft. Remove the oranges and reduce the cooking liquid to 80ml (1/3 cup). When the oranges have cooled, peel them, discarding the pips, and purée the flesh. Strain the purée and add it to the cooking liquid.
Finely shred (or cut more thickly if you prefer a chunky marmalade) approximately 100g of the peel – and add it to the cooking liquid, along with the caster sugar. Bring to the boil, add Cointreau or Chianti (if using) and reduce the heat. Simmer for about 45mins until the marmalade achieves a syrupy consistency, stirring frequently.
Test for setting: Place a small plate or saucer in to the fridge for 15mins. Pour a spoonful of the hot marmalade on to the plate and return to the fridge for 5 mins. Push the edges of the marmalade with your index finger - it is set when it wrinkles across the surface. If not set, continue to cook checking every 5mins.
The Jaffa Reds can be replaced by any Jaffa fruit when not in season - try tangerines or oranges!
Read more about Jaffa Reds in our article here