Rinse the fresh mint leaves and pat dry. Cut the lime in half; reserve one half for juicing and cut the other half into a wheel or wedge for garnish. Measure out the rum, simple syrup, club soda and have crushed ice and ice cubes ready.

Muddle mint and lime

In a sturdy highball glass or mixing glass, add the mint leaves and the juice of the halved lime (squeeze directly into the glass). Add the simple syrup. Using a muddler (or the back of a spoon), gently press the mint and lime for about 10–15 seconds — just enough to bruise the mint and release its oils without shredding the leaves (over-muddling makes the drink bitter).

Add rum and ice

Pour the light rum into the glass with the muddled mint, lime and syrup. Fill the glass about three-quarters full with crushed ice, then add 2–3 small ice cubes on top to keep it chilled.

Top with club soda

Slowly top the drink with the measured club soda, about 2 ounces (adjust to taste). If using bitters, add 1–2 dashes now and gently stir once or twice with a bar spoon to combine — lift the mint gently from the bottom as you stir to distribute aroma but avoid pulverizing the leaves.

Garnish and serve

Add the mint sprig and lime wheel or wedge as garnish. Give the mint sprig a slap between your palms to release its aroma before placing it in the glass. Serve immediately with a short straw so the drinker can sip through the mint.

Tips

Taste and adjust sweetness or acidity: add another 0.25–0.5 oz simple syrup if you prefer sweeter, or an extra squeeze of lime if you want more brightness. For a larger batch, scale ingredients proportionally. For a low-alcohol version, reduce rum and increase club soda.