Combine all ingredients in a saucepan and cook until mixture starts to boil. Let boil, stirring once or twice, for 2 minutes, and then reduce heat to medium. Continue cooking, gradually reducing heat and stirring more frequently, cook at medium heat and gradually turn to medium-low, stirring more frequently and mashing fruit slightly, until mixture reaches a syrupy consistency, about 30 minutes.

Cool and refrigerate in an airtight container for up to a month. Or transfer to two hot, sterilized 8-ounce canning jars and process in simmering water for 15 minutes; with a tight seal, jars will keep for up to 6 months.