Joan, my very elegant and very English friend shared this recipe with me; for the boiling step she uses a “jam pot” that she brought over from Britain about 50 years ago, but she assured me that my huge pasta pot would suffice 🙂 .
Scrub oranges and lemon. Cut into quarters and remove the seeds; put seeds into a cheesecloth bag. Place fruit and cheesecloth bag into a large pot with water, and bring to a boil for five minutes. Let stand, covered, for 12 to 18 hours in a cool place.
Remove fruit from the pot and scoop out the membranes, reserving any pulp or juice in a bowl – KEEP THE SOAKING WATER. Press the pulp through a sieve to remove the largest solids, and add the juice to the reserved water in the large pot. Cut the peels into very thin shreds and add the shredded peel to the pot.
Bring the pot of water, peel, juice, and cheesecloth bag to the boil again, and simmer gently for about 1 hour, until the peel is very soft and liquid is reduced by half. Squeeze all moisture from the cheesecloth bag and discard it.
Add the sugar to the pot and stir until dissolved. Increase the heat, bring to a boil, and cook until the gel point, about 5 to 10 minutes. To test the gel point, a sugar thermometer should register 220F, or put a little marmalade onto a cold saucer and place in freezer for a minute. The marmalade should feel set, and wrinkle when you push it with a finger.
“Can” as per your favourite instructions.