Make the simple syrup
- In a medium pot, combine 2 cups water with the sugar and basil and bring to a boil. Let boil until the sugar dissolves, about 2 to 5 minutes. Then turn off heat and let cool to room temperature. Remove basil.
Syrup can keep in the refrigerator for up to one month. Makes 1 pint.
Make the Basil and Grapefruit cocktail
- Combine all ingredients into a shaker, add ice, and shake vigorously. Add fresh ice into a glass, strain, and garnish with a fresh basil leaf and half of a grapefruit slice.