Place in a four quart, or larger pot, and add 1/2 cup of water to prevent plums from scorching before the juice begins to release
Heat over medium heat, and cook plums, stirring occasionally, until plums are soft
Using an immersion blender, or working in batches with a food processor, blend plums into a puree
Add sugar, cinnamon, and cloves, and stir to combine well
Place back on heat, and bring to a simmer
Continue to simmer for about 25 minutes, until puree is reduced by about 1/3. Note that this will take longer for batches that have been doubled, tripled, etc. A wider, shallower pan will also cook down more quickly than a taller, narrower one.
When plum butter is done cooking down, ladle into sterilized jars, wipe rims so that they are free of drips, or other debris, and screw down canning lids and bands.
Prepare water bath canner with hot water, and place jars in canner, making sure that the depth of the water in the canner is at least an inch over the tops of the jars
Bring canner to a rolling boil, and process half pint jars for 10 minutes (pint jars can also be used, and processed for 15 minutes)
Remove canner from heat, and let cool for at least an hour before removing hot jars
When hot jars are removed from canner, cover with a towel to protect from drafts until cooled
After 24 hours, check seal, wash jar (if needed), and store in a cool place, out of direct light