Add all the ingredients (except bitters) into a shaker with 3 ice cubes. Shake for 10 seconds and strain into a highball glass over crushed ice.
Top with bitters, garnish with a mint sprig, and serve with a straw.
Ginger Syrup
Add the sugar and water to a small saucepan over medium heat. Peel and finely grate the ginger. Once the sugar dissolves, add the ginger and simmer for 10 minutes.
Remove from heat, strain through a fine mesh strainer, and let cool to room temperature.