Peel and quarter your piece of ginger. Place in the cocktail shaker with the lime juice and muddle so the ginger pieces start to break down.
To the shaker, add the pomegranate juice, gin and simple syrup. Fill with ice cubes and with the lid securely on, vigorously shake for at least 20 seconds. Strain into a low-ball glass. Add ice and a sprig of rosemary and some pomegranate seeds for garnish.