- In a medium saucepan combine monk fruit and water. Heat over medium heat, stirring constantly, until monk fruit is dissolved. Add blackberries, raspberries, and blueberries, cover, and simmer gently for 10 minutes. Take saucepan off heat, add mint sprigs, cover, and let steep 10 minutes more.
- Strain syrup through a fine mesh sieve and stir in lime juice. Refrigerate until needed.
- To a cocktail shaker filled with ice add rum and 1oz berry syrup. Shake until well-chilled, about 12 seconds. Strain into a cocktail glass filled with crushed ice. Top off with club soda and garnish with blueberries and mint sprigs.
Note: Berry syrup may need to be shaken after chilling and right before use.