1. Cut the oranges in half and squeeze out all the juice, keeping the pips and pith that come with it.
2. Scrape out all the pith that hasn't come out when juicing and place this with the pips and pulp in a square of muslin and tie tightly.
3. Slice the orange skins into thin shreds, as thin as you like your shreds in your marmalade, and pop in a large bowl with the juice, tied muslin and top with 2 1/2 litres of water. Cover and leave overnight.
4. The next day, pop all the contents into a heavy based casserole pan or jam pan. Bring to the boil and then reduce to a simmer. You need the skins to soften so you need to leave it for about 45 minutes, maybe even longer.
5. Check the skins have softened before straining the contents of the pan. Measure the liquid - it should be about 1 1/2 litres. Boil down if more, or top up with water if there isn't enough.
6. Pour everything back into the pan except the muslin, add the skins, lemon juice, sugar and any spices (if using) and gently boil until the sugar dissolves. Skim off any froth that appears.
7. Pop a sugar thermometer in the pan (if you have one) and boil until it reaches 105°C.
8. In the meantime sterilise your jars. Wash them in warm soapy water and pop in a cold oven set to 150°C/300°F/gas 2 for 10 minutes to dry out. Or run them through a hot wash in the dishwasher.
9. When your marmalade has reached 105°C turn off the heat and test to check it has reached setting point (pop a plate in the fridge to get cold, and test to see if it wrinkles once a spoonful is placed on it. Have a read of my Figgy Jam recipe to see what I mean). Leave the pan for 10 minutes before carefully removing your sterilised jars with oven gloves and filling them with the piping hot marmalade. Be really careful as the marmalade is crazy hot! I prefer to transfer it to a jug and pour it in.
10. Seal immediately and leave to cool. The marmalade will last about 12 months but always check the lid to see if anything unsavoury is growing on there. If there is then check the marmalade before eating.