Place apple pieces, lemon juice and elderflower syrup in a cocktail shaker. Crush gently with a muddler or pestle. Add rosemary and cranberry juice. Add ice and shake vigorously for 8 to 10 seconds. Pour into a tall glass and fill with tonic. Stir gently before serving.
Courtesy of Fanny Gauthier, Ateliers et Saveurs, Montreal.