Place the 8 fresh raspberries, 20 ml simple syrup, and lime zest into a cocktail shaker. Using a muddler or the back of a spoon, gently muddle until the raspberries are broken down and have released their juices but not pulverized into complete purée (about 20–30 seconds).

Add liquids

Add 30 ml fresh lime juice, 50 ml white rum, and 15 ml raspberry liqueur (if using) into the shaker with the muddled raspberries.

Shake

Fill the shaker with about 1 cup of ice. Secure the lid and shake vigorously for 10–15 seconds until the outside of the shaker is cold and slightly frosted.

Prepare glass

Fill a highball or Collins glass with about 1 cup crushed ice (or to desired level). If you prefer a chilled glass, briefly chill it in the freezer beforehand.

Double strain and pour

Using a fine mesh strainer (or a Hawthorne strainer plus a small sieve), double-strain the shaken mixture over the crushed ice to remove seeds and large pulp. This yields a smooth drink with bright raspberry flavor.

Top and finish

If desired, gently top with 30 ml club soda for a lighter, fizzed version. Stir once gently with a bar spoon to combine.

Garnish

Garnish with a lime wheel or wedge on the rim, 2 fresh raspberries (skewered on a cocktail pick if preferred), and a mint sprig. Serve immediately.