Lillet syrup
Bring the Lillet and sugar to the boil in a small pan. Reduce the heat, add the lemon balm, simmer for approx. 5 mins., leave to cool, strain.
Cocktail
Place the ice cubes and 1 tbsp of the syrup in each glass, add the Lillet and lemon juice, top up with sparkling wine. Garnish the glasses with lemon balm.