1. Add the fresh basil leaves to a shaker and gently muddle to release the aroma.
2. Add gin, lemon juice, simple syrup, and ice cubes to the shaker.
3. Shake vigorously for about 15 seconds.
4. Strain the mixture into a glass filled with fresh ice.
5. Garnish with a sprig of basil and enjoy your Basil Smash!