This jam starts with 4 pounds of red plums, pits removed and cut into quarters (skin on). toss them in a bowl with two cups of sugar. (I use the sugar that I keep stored with a vanilla bean for baking.) Let that sit, stirring occasionally for about two hours. (This is the same method we use for apricots).
Seed half a lemon and squeeze it over the fruit. Add the lemon to the bowl and stir. Transfer ingredients to a saucepan or dutch oven and bring to a boil on the stovetop (with the lemon). Stir constantly.
Reduce heat to medium low and cook, stirring occasionally for about thirty minutes. The fruit will break down almost completely and it will miraculously turn this deep, saturated shade of red.
When it has formed a gel (place a small amount on a plate that's been in the freezer and it shouldn't run), process in half pints in boiling water canner for ten minutes. Let sit undisturbed for 24 hours, check screw bands and vacuum seal, label and store. This recipe yields about eight half pints. I find that with most fruit, a pound yields a pint of finished product.
Good times. *Possibly* the best thing I've ever eaten. I could not wait and opened a jar and just about sat and ate the whole thing with a spoon.
I find that I prefer the more tart, interesting jam flavors to the sweet, one-note ones. Next summer more apricot and red plum...YAY!