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