Begin by placing a side plate in the freezer. This will be used to test if the jam is ready.
Into a heavy bottom saucepan, use your fingers to squeeze the grape pulp out of the skin. Place the skins in a bowl and set aside. To the saucepan, add the jalapeño seeds/membrane and the rosemary. Cover and place over medium-low heat, simmer for 8-10 minutes or until pulp is soft and juicy. Strain the contents of the saucepan through a strainer to remove seeds, rosemary, and membrane. Use a wooden spoon to press down on solids to extract all the pulp and juice.
Return the strained pulp and juice to pot, add reserved skins, cover, then cook over medium-low heat for 6-8 minutes longer or until skins are softened.
Add the sugar, lemon juice, lemon zest, diced jalapeño and bring to a boil on medium-high heat, stirring regularly for 7 minutes. If the temperature of the jam has reached 220°F, it should be ready. However, add a spoonful of jam to the plate that you placed in the freezer, and let it chill for 1 minute. The jam should gel and not be runny. If not, place pot back on heat and boil for another 1-2 minutes.
Let jam rest for 10 minutes away from the heat. Then ladle into clean jars with clean 2-piece lids. Keep jars of jam in the fridge for up to 6 weeks.
** Alternatively, ladle into hot sterilized jars with new 2-piece lids. Follow normal canning guidelines and process in a boiling water canner (or deep pot) for 5 minutes, which should keep them shelf stable for a year. But seriously, these 3 little jars will not last that long!