Sterilize a glass jar in a pot of boiling water.

Rinse the fresh yuja under running water. Use baking soda and/or coarse salt to scrub the skin. Pat dry with paper towels.

Separate the yuja into peel, pulp, white pith, seeds, and juice. Discard the seeds and white pith. Thinly slice the peel into even strips.

Blend the pulp and juice (not the peel) in a blender.

In a clean bowl, combine the blended yuja with the sugar and mix well. Place the sliced peel in the sterilized jar, then pour in the yuja–sugar mixture. Stir with a clean teaspoon.

Seal the jar and leave at room temperature until the sugar dissolves. Depending on the volume, this can take a few days. Meanwhile, stir the yuja-cheong once a day with a clean teaspoon.

Refrigerate until finished. The marmalade's flavor will improve over time.

Stir 2–3 teaspoons yuja-cheong (yuja marmalade) into a cup of water until dissolved. Serve. (You can eat the yuja peel, if you like.)