Cranberry-hibiscus syrup: Heat 0.5 litres of water, 0.5 litre of sugar, 3 cups of hibiscus flowers and 2 cups of sliced fresh cranberries in a pan for 12 mins on medium heat. Stir well. Then remove from heat and strain through a sieve to remove solids. Leave to chill in the fridge. Put all the ingredients except the champagne into your shaker. Then shake together with ice until very cold. Now strain into a chilled flute glass and top it up with brut champagne. Stir with a cocktail spoon. Lemon zest serves well as garnish.