Step 1In a small bowl, combine the lime juice, lemon juice, orange juice and 1 ounce simple syrup. This makes 5 ounces sour mix.
Step 2In a pitcher, muddle the diced apple, 12 of the basil leaves and the remaining 4 teaspoons simple syrup. Add the vodka and 4 ounces of fresh sour mix, discarding the remaining sour mix.
Step 3Pour half the mixture into a cocktail shaker with ice. Shake and strain it into two chilled martini glasses. Garnish each with a Thai basil leaf and diced apple. Repeat with the remaining mixture to make two more drinks.