- 3/4 cup sugar
- 1 cup (packed) fresh mint leaves
- 1/4 pineapple, peeled, cored, cut into 1″ pieces (about 1 1/2 cups)
- 1/4 pineapple, peeled, cored, cut into 1″ pieces (about 1 1/2 cups)
- 4 limes, each cut into 8 wedges, divided
- 1/2 cup (packed) fresh mint leaves
- 2 cups light rum
- Club soda (for serving)
- Bring sugar and 1 cup water to a boil in a small saucepan, stirring to dissolve sugar. Remove from heat, add mint, and let cool completely.
- Meanwhile, place pineapple in a blender and purée until smooth.
- Strain mint syrup through a fine-mesh sieve into pineapple purée and pulse to combine. Transfer to a jar, cover, and chill.
- For each cocktail, muddle 2 pieces of pineapple, 3 lime wedges, and 1 tablespoon mint leaves in a cocktail shaker until lightly crushed.
- Add 2 ounces rum and 2 ounces pineapple-mint purée to cocktail shaker, fill with ice, cover, and shake until outside of shaker is frosty, about 30 seconds.
- Pour drink into a highball glass (do not strain) and top off with club soda. Garnish with a lime wedge and serve with a straw.
- DO AHEAD: Pineapple-mint purée can be made 3 days ahead. Keep chilled.