In a cocktail shaker, add the white coconut rum (2 oz), optional dark coconut rum (0.5 oz) if using, fresh lime juice (1 oz), coconut milk (2 oz), and simple syrup (0.5 oz).

Add mint

Add 6 of the fresh mint leaves to the shaker. Do not overfill with mint — reserve a small sprig and a couple of leaves for garnish.

Muddle gently

Using a muddler or the back of a spoon, gently press the mint leaves in the shaker 4–6 times to release the oils and aroma. Avoid pulverizing the mint to prevent bitterness.

Shake & Chill

Add ice and shake

Add a large handful of ice to the shaker (enough to chill but not overly dilute). Secure the lid and shake vigorously for about 10–12 seconds until the outside of the shaker is frosty and the coconut milk is well emulsified with the other ingredients.

Prepare glass

If using toasted shredded coconut, rim the glass lightly: wet the glass rim with a lime wedge, then dip the rim into toasted shredded coconut. Fill a highball or Collins glass with crushed ice (about 1 cup).

Finish & Serve

Strain and top

Double-strain the shaken mixture into the prepared glass over the crushed ice to remove mint solids. Top with soda water (about 2 oz) to add effervescence, pouring gently to preserve carbonation.

Garnish and adjust

Gently clap the reserved mint sprig between your palms to release aroma and place it on top. Add a lime wheel or wedge to the rim. Taste and adjust sweetness or acidity: if too tart, add 0.25–0.5 oz simple syrup; if too rich, add a splash more soda water.

Serve

Serve immediately with a straw. Encourage stirring once before drinking so the soda and coconut milk are evenly mixed.