The day before, halve the oranges and squeeze the juice. Pour the juice into a large, heavy-based pan or preserving pan and put all the pips in a bowl lined with muslin. Add the lemon juice to the pan with the orange juice.
Using a teaspoon, scrape the membrane pulp out of the fruit shells, reserving the shells, then roughly chop the pulp in a food processor or by hand and add to the pips. Tie the muslin up with string and add to the pan.
Slice the orange peels into thin, medium or thick shreds, depending on the texture you prefer, and add to the pan.
Pour 2.5 litres cold water into the pan and push the muslin bag down into the peel and liquid. Cover and leave to soak overnight to help soften the shreds.
The next day, slowly bring the mixture to the boil, then reduce the heat and simmer gently for 1½-2 hours until the liquid has reduced and the peel is very soft. Put two small plates in the fridge to get cold in preparation for testing for setting point. Once the peel is soft, lift the muslin bag from the pan and leave to cool in a bowl for 10 minutes or until cool enough to handle.
Add the sugar to the pan and stir until completely dissolved. Squeeze the muslin bag until every last bit of pectin drips back into the pan. Discard the muslin bag.
Bring the mixture back to the boil and boil for 15-30 minutes or until setting point is reached. Test by putting 1tsp of the marmalade on one of the cold plates, then leave to cool in the fridge for a few minutes. If it wrinkles when you push it with your finger, it’s ready. Alternatively, use a thermometer – it should read 105C. If it's not ready, give it another 10 minutes or so.
Remove from the heat and leave to stand for 15 minutes to ensure the peel is evenly distributed, then ladle into warm sterilised jars, cover with wax discs and seal tightly. Label and store in a cool, dark place for up to 2 years.
Recipes and photography taken from The Irish Kitchen by Cherie Denham, photography by Andrew Montgomery (Montgomery Press, £30)
