2 oz Demerara rum¾ oz lime juice, plus the spent lime half½ oz demerara syrup (2:1)3 dashes Angostura bitters8-10 mint leaves
instructions :

Combine the rum, lime juice, Demerara syrup, and the spent lime half in the chilled collins glass.

Fill the glass with crushed ice and swizzle until the glass becomes well frosted.

Finish with the bitters, and garnish with a large bouquet of spearmint. Serve with a straw.

source :
imbibemagazine.com