Combine 4 rosemary sprigs, the granulated sugar and the ⅓ cup water in a small saucepan. Turn the burner on to medium and bring the mixture to a boil. Reduce the heat and simmer for 5 minutes. Remove from the heat and allow it to cool and then strain the syrup.

In a cocktail shaker half filled with ice, combine the gin, lemon juice and 3 tablespoons of the rosemary syrup. Shake vigorously for a good 30 seconds. Strain into 4 glasses half filled with ice, top them off with soda water and garnish with a sprig of rosemary (optional).