Step 1

Muddle simple syrup and 2 mint sprigs in a cocktail shaker. Add rum and lime juice. Fill shaker with ice, cover, and shake vigorously until outside of shaker is very cold, about 20 seconds.

Step 2

Strain cocktail through a Hawthorne strainer or a slotted spoon into a tall Collins glass filled with ice. Top off with club soda; garnish with more mint.