Step 1.
- Muddle fresh basil leaves in a cocktail shaker.
Step 2.
- Add elderflower liqueur, gin, fresh lemon juice, and simple syrup to the shaker.
Step 3.
- Fill the shaker with ice and shake vigorously for 15 seconds.
Step 4.
- Strain the mixture into a highball glass filled with ice.
Step 5.
- Top with soda water and gently stir to combine.
Step 6.
- Garnish with a sprig of fresh basil.