Vanilla cherries

Name: Vanilla cherries
Yield: Makes 750 g (1 lb 11> oz)
Ingredients: 500 g (1 lb 2 oz) frozen pitted black cherries; 150 g (5½ oz) jam-setting sugar; 1 vanilla bean, seeds scraped finely grated zest of ½ lemon; 1 vanilla bean, seeds scraped finely grated zest of ½ lemon