Be sure to sterilize your jars, since you are not going to put the butter in a bath. Put plums in a pot with water and cook until skins start to split. Remove.
Remove skins and pits. Place the plums in a crock pot.
Add sugar. I put in 3 cups. I didn’t make mine too sweet. I want try making different plum sauces.
Puree the plums. Use a hand mixer or a blender. Cook on low. Could take up to 24 hours. I stir when I think about it.
As you can see the plums turn a dark brown. They are not burnt. To check to see if your butter is ready. Place a small amount on a place. If there is no liquid around it, it is ready to put in jars. Remember to fill jars to 1/4″ from the top. Be sure the jars and lids are sterile.
Turn jars upside down. I turn them back over after they have cooled. They are now sealed. You are ready to use your plum butter. Enjoy.