Wash the fruit, remove the pits before or after the first cooking step.
Place in heavy bottomed pan, lightly crushing the bottom layers to release juice.
Cook until soft.
Run fruit (including skins) through a food processor until smooth.
Return the pulp to the pan, cook on low heat, stirring frequently to prevent burning, until most of the moisture is driven out.
Put a small quantity of the butter on a plate, when no rim of liquid separates around the edge it is done.
Pour into hot sterilized jars, process according to instructions.

For an extra bit of zing, allow the fruit to ferment slightly before cooking (in other words get sidetracked for a day or two between picking and cooking). I’m told the results bear remarkable resemblance to Asian Plum Sauce.