Not everyone loves marmalade, but that's cool, because this isn't marmalade. I promise. Marmalade is justly unpopular with discerning citizens and for very good reason; there's a lot of really shitty material out there, just waiting to drag one's tastebuds on a horror ride from what is this into fucking hell get it off me territory with its puzzlingly perverse and irredeemable bitterness.
Orange jam is an entirely different thing.
As a confirmed citrus freak, I burn my oral membranes out each and every winter, sucking down every variety I can lay my greedy paws on. If you've never tasted a blood orange, you will possibly be surprised by the literal nature of their flesh and their lack of upfront acidity. Their complex, dirty undertones can creep almost toward umami; they're not super-weird, but they're not for everyone. It isn't absolutely necessary to go hunting them down for this recipe; those brilliant late winter Navels are just as good, if not better preservation prospects, due to the persistence of their high notes and clean sweetness. I like the bloods because they're a bit exotic and the colour is more intense.
Choose relatively unblemished oranges if you're concerned about aesthetics, as the skin is visible in the final result. It's not crucial, though, and you're better off sourcing wonky organic fruit sans the weird waxy crap some produce is dipped in these days to extend shelf life.
The only remotely special item needed for this recipe is a big fuck-off cooking pot that can take twelve large oranges and 3kg of sugar. The one I use is about 24cm across and 20 high, and it's still a bit inadequate, really; get a bigger one if you can.
You don't need to be anal about the quantities. Just don't use too much water or your pulp will take too long to boil down and I actually think 3L is probably more optimal than the amount quoted. The ginger quotient is up to you; we like lots and use a whole large-ish hunk of it. Leave it out altogether if you're not into it.
Please note that this recipe calls for overnight soaking of combined fruit. You can probably cut this down to a long afternoon if pressed. As a general principle, I suggest it's better to be organised and righteous than sloppy when it comes to making preserves. Botulism loves poor impulse control.
Juice the lemons. Chuck the juice, oranges, ginger and water into the cooking pot as per above pic and leave covered in a cool room or fridge overnight.
The next day, bring the fruit and water mix to the boil and keep it going at a lively roll for around 40 min. See how the pot at right is too small? Don't do that; jam burns from overflows and spatters suck dog's balls.
Remove from heat, add the sugar slowly and mix very well, keeping it off the bottom. Anything stuck there will burn horribly and ruin the jam.
12 large oranges (blood, or whatever)
3 huge or 4 medium lemons
1 medium stick of fresh root ginger
3 kilos of white sugar
3.5 L water
8-10 medium/large jars
Rigorously clean all the fruit, ginger included. No need to peel the latter unless you're one of those people.
Look the oranges over for soft spots, nasty bits and mould; don't waste the whole fruit, just cut a wide margin around these blemishes. I top and tail the oranges to eliminate annoying thick pieces in the final result but that's up to you.
Cut all oranges in half, then half again and then into narrow strips, remembering the final thickness of rind will persist in the result, so think about the dimensions you prefer. Slice the ginger down to whatever thickness pleases you.
Return to heat and stir fairly regularly to make sure everything's dissolved. Keep it on a medium boil for another 40-60 min until it reduces to around two thirds (as per left pic) and starts bunching on the spoon and cool-setting. You might need or prefer to boil for longer depending on how thick and sticky you like the jam; I prefer runny, so come out at around 50 min. (The jam will set further in the fridge once opened so don't panic).
Importantly, you should let this jam rest in the pan, off heat, for around 10 mins to cool before filling your jars, so the orange pieces don't all float to the top- I was a bit impatient and you can see it in pic below.
Mine still slops around in the jar after a notional set, but you can boil it down to rubbery firmness; while I personally think this is gross, you're the one eating it. We like to spoon it out and let the syrup soak into the toast while the fruit sits on top, smiling at you. Refrigerate once opened. Use liberally in poultry recipes, sauces and on cakes, too.