Peel and chop nectarines (you can blanch them first for easier peeling).

Combine nectarines, sugar, and lemon juice in a saucepan.

Cook over medium heat, stirring frequently, until fruit softens (about 10 minutes).

Mash with a potato masher for a chunkier texture or blend for smooth jam.

Add pectin (if using) and bring to a full rolling boil for 1–2 minutes.

Simmer until thickened, about 20–30 minutes, stirring often.

Pour into sterilized jars. Let cool, then refrigerate or process in a hot water bath for long-term storage.