1. To prepare syrup, combine all ingredients in medium saucepan. Bring to a light boil while stirring constantly. Reduce heat to low and let simmer 20 minutes. Remove from heat and let cool.
2. To prepare cocktail, add gin, both juices, and syrup to shaker. Add ice. Shake and strain over fresh ice and top with sparkling wine. Garnish with sprig of fresh basil.