Pit plums; do not peel. Chop or leave in halves. Measure 4 cups into a 6- or 8- quart sauce pot. Add lemon juice, orange juice, honey and cardamom (if desired).
Prepare jars (wash, inspect rims, clean in sink or dishwasher). Keep lids warm until ready to fill jars.
Bring plum mixture to gentle boil on medium heat, stirring frequently to prevent sticking to the bottom of the pot. Continue to cook and stir until plum jam reaches desired thickness. (Remember, jam will thicken as it cools.)
Skim off any foam with a metal spoon, if desired. (I usually skip skimming.)
Ladle quickly into prepared jars, filling to 1/4 inch of top. Wipe jar rims and threads. Cover with two piece lids.
Process jars for 10 minutes in a boiling water bath canner. When processing time is done, let rest a few minutes in the water bath, then place jars on a towel on the kitchen counter. Allow to cool completely.
Remove rings for storage. Wipe tops and test seals. Date and label and store in a cool, dark location. Best if used within 1-2 years.
Keywords: jams and jellies, plum, easy, low sugar, honey sweetened