Chef John's Kumquat Marmalade
If marmalade is not your favorite type of fruit preserve, it's most likely because of those bitter flavors from the white parts of whatever type of citrus was used. That is not an issue with this gorgeous kumquat marmalade.
Measure the kumquats after you've removed the seeds and membrane and sliced them.
You can just go by appearance, but I took the temperature right before it was done, and it was about 215 degrees F (100 degrees C), so I imagine when I was finished it was around 220 degrees F (105 degrees C). You can also put a spoonful on a plate in the fridge, and test that way.