Add raspberries, blackberries, and basil leaves to the shaker or mason jar. Muddle gently until the berries release their juice.
Pour in the lime juice and simple syrup. Fill the shaker halfway with ice cubes.
Shake vigorously for 15-20 seconds until well chilled.
Strain the mixture into a tall glass filled with fresh ice. Top with sparkling water.
Stir gently to combine. Garnish with fresh berries and a basil leaf.
Notes
Store simple syrup in the fridge for up to 2 weeks. Make it by combining equal parts sugar and water, and heating until dissolved.Fresh berries work best, but frozen can be used in a pinch. Thaw them first.The drink is best served right away while the sparkling water is fizzy.For a sweeter drink, add an extra 1/2 oz of simple syrup.