Fill a sling glass to the top with crushed ice
Place 6 red basil leaves into a shaker
Pour 0.5 oz of lemon juice, 1.25 oz of sugar syrup, 0.5 oz of blackberry liqueur and 1.5 oz of gin into the shaker
Fill the shaker with ice cubes and shake
Finely strain into the sling glass
Top up with club soda and stir gently
Top up with crushed ice
Garnish with a red basil sprig and a Maraschino cherry