Step 1

Bring sugar and 80ml water to the simmer in a saucepan over medium heat, stirring to dissolve sugar. Remove from heat, cool to room temperature, then refrigerate until chilled.

Step 2

Bruise mint lightly with your fingers, then place in four chilled tumblers. Lightly swirl around with a muddling stick, set aside.

Step 3

Place ice in tumblers, piling high above the rims.

Step 4

Pour sugar syrup over ice, dividing among tumblers, then divide bourbon among drinks. Garnish with a large sprig of mint and serve with a drop or two of bitters.