Slice off the tops and bottoms of the mikan, and cut off the outer skin down to the membranes to remove the flesh. After cutting off the membrane from the perimeter, use a knife to easily remove the inner pieces.

Put the mikan in a saucepan, sprinkle sugar on top, and when the sugar dissolves, bring to boil.

After it comes to a boil, reduce to low heat, and simmer while stirring continuously without stopping. Be diligent about skimming the scum at the top.

Since there is a high water content, you can heat on medium-high heat. It's done when it's thick enough to see the bottom of the saucepan when mixing.

Transfer to a sterilized jar and it's ready to serve.