Clean, rinse and pit the cherries. Cut half in half, mash the rest with the juice of one lemon until mushy.
Place fruit and fruit puree in a large saucepan. Slit vanilla beans lengthwise, scrape out pith. Add the vanilla pods and the vanilla pulp with the preserving sugar to the fruit. Bring to a boil while stirring. Bubble for 3 minutes.
Fold in the sherry. Boil the mixture again briefly and skim off the foam.
Remove the vanilla pods and fill the fruit mixture hot to the brim into the jars.