Add basil leaves and simple (or honey) syrup to a shaker and muddle gently to release oils.
Add vodka (or gin), fresh grapefruit juice, and a handful of ice.
Shake 10–15 seconds until well chilled, then fine‑strain into a rocks glass filled with fresh ice.
Garnish with a basil sprig or grapefruit wedge and serve immediately.
Notes
Pink grapefruit gives a softer, less bitter profile and a pretty hue. Swap vodka for gin for a more botanical vibe. For a lighter drink, add a splash of sparkling water. Avoid over‑muddling basil to prevent bitterness.