Soak the peels in water for 4 ~ 5 hours (while changing the water occasionally.) Drain the water, and weigh the peels.
Pour enough water to cover the peels in a pot, and turn on the heat. Simmer until the peels soften (for about 15 minutes). When the peels soften, add yuzu juice, then add the sugar which is 60% weight of the juice + peels. Simmer until thickened.
Pour the jam into disinfected jars while it's still hot.
Story Behind this Recipe
I made this jam because I was given a lot of yuzu as a gift.
I recommend not making too much. (It's hard to make and store a large amount.) Make sure that you taste it, and if it's sour, increase the sugar to your liking. It hardens when cooled, so turn off the heat when it's still a little bit runny. The key is not to simmer for too long.