To Prepare the Juice:
Crush fully ripe plums. (Do not peel or pit). Add 3/4 cup of water, bring to a boil, simmer, covered, 10 minutes. Place in jelly cloth or bag; squeeze out juice. Measure 3 cups into very large saucepan.
To make the jelly:
Measure sugar; set aside. Place saucepan holding juice over high heat. Add powdered fruit pectin; stir until mixture comes to a hard boil. At once stir in sugar. Bring to a full rolling boil; boil hard 1 minute, stirring constantly.
Remove from heat, skim, pour quickly into glasses. Seal at once.
Notes
*note recipe indicates using Paraffin to seal the jars. That is an outdated way of canning/ preserving. I have purposely left out processing time to make the jelly "shelf stable". Instead I would suggest storing the jelly in the refrigerator.