Pick ripe but firm fruit, wash them carefully, dice or chop and heat in a large pot.
Add 3 pounds of sugar for each pound of fruit, mix and boil at medium temperature, stirring occasionally.
(Temperature should be such that the mix shimmers constantly, but does not boil over)
Skim the foam that forms on the top.
Turn heat off when it is as thick as honey. It will gel more as it cools.
Put in jars while still shimmering, and close the lids. The lids will "pop-in" as it cools, and the negative pressure along with the sugar will conserve the jam for a long time.
After opening, keep in the refrigerator, because this version uses less sugar than commercial marmalade (50% or more sugar to fruit ratio), so it needs refrigeration to stay good.