1 1/2 lb. Frieda's Adorable kumquats
1 naval orange
5 cups water
2 cups sugar
Pinch of sea salt
Special equipment: candy thermometer
Halve kumquats, remove and preserving seeds*, then roughly chop. Slice orange into rounds, remove and discard seeds, and roughly chop. Place chopped fruit and their juices in a non-reactive saucepan. On a cheesecloth, add reserved kumquat seeds to make a bundle, then add the bundle to the saucepan. Add water. Bring the mixture to a boil, remove from heat, cover, and let sit for at least 4 hours or overnight. Add sugar to the mixture and cook over medium heat for 30-45 minutes. Remove the seed bundle and carefully press the bundle to release extra juices into the mixture. Continue to cook until the mixture reaches a gel point of 220 degrees F, or until desired thickness. Remove from heat. Skim off any scum or foam. Stir in sea salt. Pour into clean jars and store refrigerated for up to 2 weeks.
For shelf-stable jam, follow canning manufacturer’s guidelines and instructions.
*There is a lot of pectin in the seeds that will help the marmalade "gel." If you don't want to take this extra step, go ahead and discard the seeds.