Place the juice from the cherries in kirsch(just the liquid), plus the cherry juice into a small saucepan. Bring to the boil, then simmer until reduced by approx one third (takes around 20 minutes).
Leave to cool, then add the cherries back in and blend using a hand blender. At this point you can cover and refrigerate for 1-2 days until ready to use.
To decorate the glasses, slice a lemon in half and run the lemon around the rim of the glasses. Mix together the sugar and gold glitter/lustre on a small plate, and dip the rim of the glasses in this sugar mixture.
When you're ready to serve, fill around ⅓ of each glass with the black cherry puree. Top up with prosecco or champagne. Thread 2-3 cherries through a skewer and place in each glass to decorate before serving.
*I use Opies black cherries in kirsch. If you can't find them, you can use de-stoned tinned/canned black cherries in juice. Use the cherries, half the juice plus 4 tbsp cherry brandy..Nutritional Information is per serving.