Found the easiest recipe in Joy of Cooking. I bought their special All About Canning & Preserving a couple years ago (last year?). I think the recipes are identical to the Joy of Cooking. But they have lots of pretty pictures!
Plum Jam (bottom right on picture)
- 2# plums, chopped to desired size (about 8ths for me)
- 2.5 c sugar
- 1/4 c bottled lemon juice
* I couldn't figure out how to skim off foam from any of my jams. I would have removed half the jam! Some recipes call for up to a teaspoon of butter to reduce foaming. I didn't think it worked until I tried one recipe with and one without (Peach-Plum on bottom left of picture, it's light colored because of the foam). The without didn't only have foam on the top, but all the way through the jam. I will put 1/2-1 tsp of unsalted butter in all my jams going forward. Except this one. It didn't get very foamy.
I made this three times because we loved it. I made each batch separately, as elsewhere, I've been cautioned to never double a jam recipe. The last time I made jam, I scorched it (grape jelly, which I still have because I can't stand to part with something that took so much work. But yet I don't want to eat it either. Silly me.) or didn't cook it long enough (strawberry ice cream topping instead of jam). But this time, I got it!
I also found out that our thermometer probe doesn't work. The first batch was boiling away merrily...but the thermometer registered only 212 degrees. It's supposed to get up to about 220 for the jelling stage. Thankfully, I decided after a while of that to test it and it was there. So I tested some boiling water. The temp registered around 202, off by 10 degrees! Time to get a new thermometer. I want an instant read one anyway; this one you have to wait a couple minutes to register, which is a pain on things like bread where you have to put them back in the oven. Might also be why my bread was always so hard; I over baked it!
I also dried some plums. The first time out of the dehydrator, I thought they were very sour--the peel was overpowering. Since they dry unevenly, I take them out, put them in a container for a day or two, them dry them again. The second time, I thought they were a lot better. Not quite like the prunes you get in the store these days (which they called dried plums now), but quite good. I should make some more, if my plums aren't too squishy.