Over medium heat dissolve the Granulated Sugar (4 tablespoon) in the Water (125 milliliter). Strip the leaves from the Fresh Rosemary (2 sprig) and roughly chop to release their oils.
Add to the syrup and allow to reduce and infuse for 10 minutes over low heat. Strain to remove the leaves the leaves and let the syrup cool completely.
In a cocktail shaker, add one part Musgrave® Gin (50 milliliter), a decent handful of ice and 50 milliliters of the rosemary syrup. Shake to combine and pour into a long glass to about halfway up. Add a few ice cubes and top up with Tonic Water (to taste). Stir, serve, and enjoy!