This is the recipe for my Grandma’s Lattwerk. It will yield about 4 pints.
The night before mix 5 pounds of pitted Italian plums with 1 pound of sugar. Add 1 cinnamon stick and 1 or 2 star anise in a little muslin bag. Let sit overnight.
In the morning stir the plums, bring them slowly to a simmer and do not stir. (My Grandma always claimed, that the preserve would burn, if you stir it. Do you want to risk it?)
Once it simmers I turn the stove on low and let it bubble gently for 6 to 8 hours.
Now the tricky part: According to Grandma the preserve is done, when there is a skin on the surface. Honestly I am not sure what she meant by that. You will find the preserve reduced to about half. There will be many “flat” plums on the surface and the liquid will be thickened.
Take a leap of faith, stir the preserve and fish out the spices. Ladle into jars and process for 10 minutes.