Prepare an ice bath, boil a large pot of water and blanch plums for 20-30 seconds until skins start to peel back. Remove plums to ice bath with a slotted spoon.
Peel off skins and cut plums into chunks off of the pits
Place plum chunks, honey, sugar, rosemary and ⅔ cups water in a medium saucepan and bring to a boil, reduce to medium-low and simmer for about 35-40 minutes, until thickened and resembles a syrup-like consistency. Skim the top often while simmering.
Ladle into jars (mine made 2 8oz Ball jars full), seal and refrigerate.
Recipe by Jackie Ourman at https://jackieourman.com/yellow-plum-local-honey-and-rosemary-jam/