Add the plums, sugar, and lemon juice to your pot and add water to about 1/4-inch depth. Cook over medium heat, stirring frequently, until thickened. (You can eye-ball it, but you're going for about 218 - 220°F on a candy thermometer (adjust down about 10 degrees for 5000 ft. elevation).)
Recipe Notes / Tips
Refrigerate. Keeps at least 2 weeks.
Sour Cherry Jam: same proportion of fruit to sugar + lemon juice
Try with figs, strawberries, or other fruits in season
Optional: After cooking, add a spoon of balsamic vinegar or liqueur