Combine all ingredients—chopped apricots, apple cider vinegar, both sugars, minced red onion, grated ginger, mustard seeds, red pepper flakes, and salt—in a large, heavy-bottomed non-reactive saucepan or Dutch oven.

Bring the mixture to a rolling boil over medium-high heat, stirring occasionally to ensure the sugar dissolves completely and nothing sticks to the bottom.

Once boiling, reduce the heat to maintain a steady simmer. Continue to cook, stirring every 5-7 minutes, for approximately 40 to 45 minutes.

The chutney is done when it has thickened significantly and coats the back of a spoon. The apricots should be soft but still hold some shape; the mixture will thicken further upon cooling.

Remove the pan from the heat. Allow the chutney to cool slightly before transferring it to sterilized jars. Seal the jars tightly.

Store the chutney in the refrigerator. It is best after resting for at least 24 hours, allowing the flavors to meld. Keeps well refrigerated for up to 3 weeks.