Usually I make a basic plum jam recipe that uses 2.5kg plums (stones removed). Add 1 1/4 cups water and cook slowly until the fruit is pulped. Add 2kg sugar and boil quickly for 20-30 minutes. Test a little on a cold plate to see if it sets. Spoon into sterilised jars. Makes about 8 large jars.
You can use ~2.7kg whole plums and simply remove the stones as the mixture cooks.
I also found a recipe for Spiced Plum Butter which is very tasty. I now make a combination of the two that involves blending the plums a bit (with a stick mixer) and adding spices to the basic recipe. The original recipe is below.
1 cup water
1 cinnamon stick
4 whole cloves
1/2 tsp ground nutmeg (optional)
Place plums and water in a medium stainless steel or enamelled saucepan. Bring to a full boil over high heat, cover, reduce heat and simmer for 20 minutes or until plums are tender, stirring occasionally.
Place plum mixture in a food processor or blender and process until almost smooth. Measure and return to saucepan. For each 1 cup (250ml) plums, add 1 1/4 cups sugar. Tie cinnamon and cloves in a spice bag and add to saucepan.
Return plum mixture to a boil, reduce heat and boil gently, uncovered, until mixture is very thick, stirring frequently (about 1 hour).
Discard spice bag; stir in nutmeg (if using).
Ladle into hot sterilised jars. Makes about 3 cups.
The recipe actually says to “ladle into hot jars and process for 10 minutes using a canner”. It is an American book and every recipe seems to process the jars in a canner. More about this in another post, but every other recipe I’ve seen for plum jam (in NZ at least) simply puts it into sterilised jars. It has been absolutely fine for me.