Plum Jam

Directions

1. 1
   Combine ingredients in a large pot and cook over medium heat, stirring frequently, until the mixture starts to resemble jam - i.e., when you drag a spoon or a spatula along the bottom of the pot, the separation remains for a bit before the syrup fills it in (this should be about 220 degrees on a candy thermometer, but it's OK if you're a little on the low side).
2. 2
   Meanwhile, sterilize 4 1/2 pint canning jars by boiling them in water.
3. 3
   Fill the hot jars with hot jam, leaving 1/4 inch at the top, wipe the rims clear of any jam to get a good seal, and put on the caps and rings.
4. 4
   Boil in rapidly boiling water for 10 minutes with the jars entirely covered with water but ideally not touching the bottom of the pan and with the caps and rings tightly on.