Remove the pits from the cherries with a knife or cherry pitter.
Add all ingredients to a pot.
Stir it together, bring to the boil, then reduce the heat and simmer for 15 minutes, until the cherries start to break down.
Place a fine-mesh strainer over a bowl or jug and pour in the mixture. Press the cherries into the strainer to extract as much cherry syrup as possible.
Allow the mixture to cool, then pour into a jar or bottle and keep in the fridge for up to 2 weeks.