Remove the lid and cook for another 5 minutes or until the cherries are softened and the outside look a bit wrinkle. Using a slotted spoon, transfer them to a medium heatproof bowl. Continue to reduce the juice until thick enough to coat the back of a spoon, about 15 minutes, stirring often. Transfer the juice to the bowl with the cherries. Stir in vinegar, salt & black pepper. Taste and adjust. Let it cool at room temperature for 30 minutes. Transfer to an airtight container and keep in the fridge until ready to use.