Wash the hassaku oranges (I used some pesticide-free oranges that I had been given) and peeled away the orange-coloured part. Shred and weigh the peel (82 g in this case) and boil and drain it a couple of times to reduce the bitterness.
Remove any remaining peel with the pith (white parts) until you just have the actual fruit remaining.
Take apart the segments. When doing this, push each segment upwards, as shown in the picture, to avoid losing too much juice. Weigh the total weight of the segments. In this case it was 750 g.
Weigh out the sugar to an amount that equals 45% of the total weight of the hassaku orange fruit and peel (which was 375 g here). Add everything to a pot and place over a medium heat.
Mine turned out like this. It might have been better to have removed it from the heat a little earlier though. It became quite a sticky marmalade. But since I removed all of the pith, it's also become a brilliant orange colour.
Story Behind this Recipe
I was given lots of hassaku oranges.
The pith has a very bitter taste but if you like that feel free to shred in the pith along with the skin. It'll make the fruit easier to shred that way. You can adjust the amount of sugar. I only used 45% because that's the sugar content of regular store-bought jam. If you use a bigger pot the water will evaporate faster so you'll be able to finish making the jam more quickly.