To make mint simple syrup, in a small saucepan bring Water (1/4 cup) to a boil. Remove from heat and add Granulated Sugar (1/4 cup) and stir until dissolved. Throw in half of Fresh Mint Leaves (20) and let it sit for at least 15 minutes.
In a medium bowl, add remaining Granulated Sugar (1 tablespoon) and remaining mint leaves (20). Bruise the mint leaves with a muddler. Stir in mint simple syrup, Lime Juice (1/4 cup), White Rum (1/2 cup), and Coconut Rum (1/2 cup).
Pour the mixture into a pitcher with Ice (2 cup) and Club Soda (2 cup) right before serving.