Prepare the fruit: Combine the chopped nectarines, sugar, and lemon juice in a large, heavy-bottomed saucepan. Stir well to combine.

Infuse the vanilla: Scrape the seeds from the vanilla bean pod into the fruit mixture. Add the scraped pod to the pot as well.

Cook the jam: Place the saucepan over medium-high heat. Stirring constantly, bring the mixture to a rolling boil that cannot be stirred down. Once at a full boil, stir in the pectin briskly over the heat.

Achieve setting point: Continue to boil hard, stirring frequently to prevent scorching, for another 5 to 10 minutes, or until the jam reaches 220°F (104°C) on a candy thermometer, or passes the freezing plate test (a small spoonful placed on a chilled plate wrinkles when pushed).

Finish and jar: Remove the saucepan from the heat. Carefully remove and discard the vanilla bean pod. Skim any foam from the surface. Ladle the hot jam into sterilized half-pint canning jars, leaving 1/4 inch headspace.

Process the jars: Wipe the rims clean, affix the lids and screw bands until fingertip tight. Process in a boiling water canner for 10 minutes, adjusting for altitude. Remove jars and let cool completely before checking seals.