Remove the buttons from the oranges and scrub them in warm water. Dry.
Cut the oranges in half, around the middles, and squeeze out the juice. Squeeze the lemons as well (or add the lemon juice).
Don't discard the white pith and the pips of the oranges, insted place them into a muslin bag. You can also use an old pair of tights to do this!
If there are any stringy bits left inisde the orange halves, use a spoon to carve them out and remove them. Place them into the muslin bag (or old tights!) as well.
Fill your jam pan with 2.25 litres of water
Strain juice of oranges and lemons into the jam pan.
Add any pulp and pips from the sieve into the muslin bag and tie tightly.
Add muslin bag to the pan of water and juice.
Cut orange peel into strips (cutting the hemispheres in half first makes this easier).
Strips can be anywhere from wafer thin to about 3mm wide, but best to be consistent with your size.
Add peel to the jam pan and cover, leaving overnight.
Bring the pan up to a bubble and leave simmering for 2 hours
The peel should now be soft and the liquid reduced by about 1/2
Remove the muslin bag, squeezing out any extra liquid.
If you have a measure on the side of your preserving pan, you'll want about 1.5-1.75l of liquid and peel. To aboid overcooking your sugar, reduce the liquid down until you are within this range.
Place your jars and lids into a preheated oven at 140 °C / 275 °F (120 °C / 240 °F fan).
Add the sugar to the pan and gently stir until it has dissolved.
Once it has dissolved, turn the heat up to maximum and bring the jam to a rapid rolling boil.
When the jam has reached 105c/220f, test for set. If you don't have a sugar thermometer, boil for 5 minutes before testing.
Remove the pan from the heat, and place a teaspoon of the jam on a cold plate.
After a couple of minutes, push the jam with your finger. If it wrinkles, and doesn’t flow back into the gap, you have achieved a set.
If not, return the pan to the heat for 2 more minutes and try again.
When the surface of the jam is still, remove any scum from around the edges.
Then give the jam a thorough stir, to disperse any remaining scum and to speed up cooling.
Leave for 10-20 minutes, until the peel is suspended in the jam, rather than floating on the surface.
Remove your sterile jars from the oven, remembering not to touch the inside.
Use a jam funnel and ladle to fill the jars, and place the lids on, remembering not to touch the inside. A magnet can help to lift the jar lids from your baking sheet.
Secure the lids and leave to cool completely.