Just made Rhubarb Jam from the Blue Chair Jam Cookbook, and it's a treat. It's just rhubarb, white sugar & lemon juice. I cut back on the sugar a little; I'm really happy with the result.
The paraphrase is below. I highly recommend the book.
4 lbs trimmed rhubarb cut into 3 - 4 inch lengths
2 3/4 lbs white sugar
3 ounces strained fresh lemon juice
Mix all ingredients & let macerate for 24 hours at room temperature.
Transfer to 11 to 12-quart copper preserving pan or similar.
Bring to boil over high heat & boil, stirring frequently until thickened and no longer watery, about 20 minutes.
Test for doneness - her method is to put some on a frozen spoon, to put the spoon back in the freezer for about three minutes, and then to test it by seeing if the jam on the spoon runs when you tilt the spoon vertically.
Skim any foam from the surface of the jam, put in jars & process appropriately.