Step 1

Place 1 cup water, 1 cup granulated sugar, 1/4 cup umeboshi paste (or 6 pickled plums), and 2 tablespoons rice vinegar in a small saucepan. Bring to a boil over high heat, whisking the mixture to combine. Reduce the heat to medium-low and simmer until the liquid thickens and reduces to about 1 cup, 35 to 45 minutes.

Step 2

If using whole plums, remove and discard them. Transfer the sauce to a bowl and let cool.