Make a simple syrup in a small saucepan: bring sugar and water to a boil; simmer until the sugar is dissolved, 3 minutes. Remove from the heat and let cool completely. Place everything and 20 ml of simple syrup but the tonic in a cocktail shaker. Shake well and strain into a glass filled with ice cubes. Top up with tonic.
Courtesy Romain Cavalier, Grand Prize Winner, Made with Love 2015.