Pour 10ml  of the mint syrup into a chilled glass. Combine bourbon and ice in jug of a blender, blend until smooth.

Spoon bourbon mixture into glass, stir, drizzle with remaining mint syrup.

Glass 300ml highball

Garnish a straw

*mint syrup: fill a large ball with ice and water. Bring a small saucepan  of water to a boil. Plunge 2 cups firmly packed fresh mint leaves into boiling water for about 3 seconds. Remove with a slotted spoon, then immediately transfer to iced water until cold, drain.
Combine 180ml sugar syrup and mint in a blender jug, blend until pureed, stand syrup for 10 minutes. Push syrup through a fine sieve, pressing down firmly to extract as much liquid from mint as possible, discard mint pulp.

Store in an airtight container for up to a week in the refrigerator.

Makes about 180ml