Step 1In a large, heavy-bottom pot, stir together the nectarines and sugar until thoroughly combined. Warm over medium heat, stirring occasionally, until the mixture is liquid and flowing. Bring the mixture to a full boil, stirring occasionally to keep from sticking. Remove the pan from the heat, stir in the lemon juice and set aside for at least 8 hours to give the fruit time to macerate. If you're going to leave it for more than a day, refrigerate after 8 hours.
Step 2When you're ready to finish the jam, ladle two to two-and-a-half cups of fruit and syrup into a nonstick skillet and place over medium-high heat. Add the lemon verbena and cook, stirring constantly, until the mixture falls from the side of a spoon or spatula in sheets, or until a drop of the mixture spooned onto an ice cold plate gels and is firm, about 3 to 5 minutes (add 2 to 3 minutes if the mixture has been refrigerated).
Step 3Spoon the mixture into a container and refrigerate until ready to use. If you prefer to can traditionally, you can follow the instructions from the jar manufacturer.
Step 4Repeat with remaining fruit and syrup.