Prep your glass: Use a tall highball or Collins glass.
Add the sugar (or simple syrup) and freshly squeezed lime juice.
Add mint: Place 8–10 mint leaves into the glass. Gently press them with a muddler or the back of a spoon for 5–10 seconds—just enough to release fragrance, not shred the leaves.
Add rum: Pour in 2 ounces of white rum and give a quick stir to dissolve the sugar.
Ice it: Fill the glass with ice. Crushed ice gives more dilution and a frosty feel; cubes keep it a touch stronger and fizzier.
Top with bubbles: Add club soda to fill, about 2–3 ounces.
Stir gently from the bottom to lift the mint and integrate flavors.
Garnish and serve: Slap a mint sprig between your palms to release aroma, then tuck it into the glass with a lime wheel or wedge. Serve immediately.