Bring to a boil (this will likely take about 5 minutes). Gently stir again, then lower the heat to medium-low, cover, and simmer for 15 minutes, until the prunes are soft and swimming in syrup.
Transfer the stewed prunes to a heat-proof glass storage container. Cool to room temperature, about 15 minutes, then cover and refrigerate for at least 1 hour. This allows the syrup to thicken and flavors to develop. Serve alone as dessert, or spoon on top of plain Greek yogurt.
Stewed prunes are wonderful when served warm, but you can also eat them cold, after being refrigerated overnight (or longer). The advantage of refrigerating them is that it considerably thickens the cooking liquids and makes them more syrupy.