Combine the diced nectarines, sugar, apple cider vinegar, grated ginger, sliced chili, mustard seeds, cinnamon, and salt in a large, heavy-bottomed saucepan.

Bring the mixture to a boil over medium-high heat, stirring constantly until the sugar is completely dissolved.

Once boiling, reduce the heat to low and let the chutney simmer gently. Do not cover the pot.

Cook for 40 to 45 minutes, stirring occasionally to prevent sticking. The chutney is done when it has thickened considerably and coats the back of a spoon. The nectarines should be soft but still retain some texture.

Remove from heat and allow to cool slightly. The chutney will continue to thicken as it cools.

Taste and adjust seasoning if necessary (add more salt or a dash of vinegar for brightness, if desired).

Transfer the chutney into sterilized jars, leaving about ½ inch of headspace. Seal tightly and refrigerate. It will keep well for up to three weeks.