- Peach-Basil Syrup:
- 4 ripe unpeeled peaches, pitted and coarsely chopped
- 1 1/2 cups white sugar
- 1 cup water
- 3 sprigs basil, tied together with string
- Cocktail:
- ice cubes, divided
- 1 1/2 fluid ounces bourbon
- 3 dashes aromatic bitters (such as 18.21 Prohibition Aromatic Bitters)
- 2 fluid ounces lime-flavored sparkling water (such as La Croix®)
- 1 slice peach
- 1 leaf basil
- Combine chopped peaches, sugar, water, and 3 sprigs basil in a small pot over medium heat. Simmer, stirring occasionally, until sugar dissolves, about 5 minutes. Cool syrup to room temperature, about 10 minutes. Discard basil sprigs.
- Pour syrup into a Mason jar, seal, and refrigerate until completely chilled, about 1 hour.
- Measure 3 fluid ounces of syrup and peaches into a cocktail shaker; muddle to break peaches up. Add 4 ice cubes, bourbon, and bitters; cover and shake vigorously until ice is mostly melted. Pour into a chilled 8-ounce glass; add remaining 4 ice cubes. Gently stir in sparkling water. Garnish with a peach slice and basil leaf.