Place the diced persimmons in a small saucepan. Add the juice of ½ a lemon and mix well. Cook for 5 minutes over medium-low, regularly mixing. Use a fork or a potato masher to mash the persimmons.
Add the sugar and salt. Continue to cook and mix until the sugar dissolves.
Lower the heat to a simmer and cook for 10 minutes. Mixing occasionally.
Continue to cook in increments of 5 minutes until most of the juices have evaporated and a thicker concisely is achieved. This will vary depending on how juicy the persimmons are.
Use the fork or potato masher one more time for a smoother texture.
Remove from the heat, transfer to an air-tight container, and allow it to cool completely before storing it in the refrigerator.
Notes
Make sure to use very ripe persimmons: Especially if using astringent varieties like Hachiya. Taste the fruit, as one unripe fruit can ruin the batch.
Enjoy is smooth or chunky: For smooth jam, puree the fruit before or after simmering. For chunkier jam, hand-mash it to your desired consistency.
For a longer shelf life: Follow the recipe as written and use sterilized jars. Reducing the sugar/lemon can affect the shelf life.