Muddle the basil and lime: In a sturdy glass, add the basil leaves and a lime wedge. Gently muddle 3–4 times to release oils and juice.
Don’t grind it to a paste—light pressure is enough to keep the flavors bright, not bitter.
Add lime juice and sweetener: Pour in the fresh lime juice and simple syrup. Stir to dissolve. If using granulated sugar, stir an extra 10–15 seconds so it blends fully.
Build the base: Add white rum and coconut rum.
For a creamier style, swap the coconut rum for coconut milk. Stir briefly to combine.
Ice it up: Fill the glass with ice. Crushed ice gives a frostier, beachy feel; cubes melt slower and keep the drink brighter longer.
Top with bubbles: Add club soda or sparkling water.
Give it a gentle stir from the bottom up so the basil and lime don’t all float away.
Garnish and serve: Smack a basil sprig between your hands to release aroma, then tuck it in. Add a lime wheel or a pinch of toasted coconut for flair. Serve immediately.