How to Make It
Combine first 3 ingredients in a large bowl, stirring well and mashing fruit with the back of a wooden spoon to release juices. Cover tightly, and refrigerate 24 hours. Stir in vinegar. Cover tightly, and refrigerate 3 hours. Stir well, and strain through a fine-mesh sieve, pressing gently on solids. Discard solids.
To prepare each cocktail, combine 1 1/2 ounces gin, 1 ounce vinegar mixture, 1 ounce club soda, and 1/4 ounce fresh lemon juice in an ice-filled shaker. Shake vigorously 30 seconds; strain into a Collins glass. Garnish with a lemon twist and fresh basil leaves, if desired.