For the cucumber vinegar:
1/2 cup sliced cucumber with peel on
1 cup unseasoned rice wine vinegar
For each soft cocktail:
2 shiso leaves, plus 1 more for garnish
8 fresh mint leaves
1/4 ounce simple syrup
3 ounces fresh Granny Smith apple juice
1 ounce Cucumber Vinegar
1/4 ounce fresh juice from 1 lime
To make the cucumber vinegar:
In a small bowl, combine cucumbers and rice wine vinegar. Let stand 5 minutes, then strain.
To make the fresh apple juice:
Add two ounces water to a blender, then add 1 chopped unpeeled Granny Smith apple gradually to the blender. Blend until uniform, then strain through a fine-mesh strainer. Use immediately.
To make the cocktail:
Add shiso, mint, and simple syrup to a highball glass. Muddle, pressing gently, until you smell the mint fragrance. Add apple juice, cucumber vinegar, and lime juice and fill glass with ice. Stir until well chilled, about 10 seconds. Top with a splash of sparkling water. Garnish with a shiso leaf and serve immediately!