Step 1

Make sugar syrup. Cut lime into quarters; place 6 lime wedges into cocktail shaker. Using muddler, crush lime wedges with sugar syrup and sprigs of mint. Add rum and ice; shake vigorously.

Step 2

Strain into four 125ml glasses; top with soda water. Add remaining lime wedges and extra mint leaves to glass.

Step 3

Stir 1 cup caster sugar with 1 cup water in small saucepan, over low heat, until sugar dissolves; bring to the boil.

Step 4

Reduce heat; simmer, uncovered, without stirring, 5 minutes. Remove from heat; cool to room temperature. Store in an airtight container in the fridge for up to 1 month.