Dissolve the sugar and water in a small saucepan over medium heat then add the dried hibiscus.
Once it turns a deep red color, add the washed Thai Basil leaves and continue cooking over medium low heat for 4-5 minutes, stirring occasionally.
Let it cool completely BEFORE straining so that the flavors can continue to steep as it cools. You can save the rest of this syrup in the fridge for up to 1 month.
Since this is technically a rich syrup, I recommend using 3/4 oz for this recipe but you can up it to 1 oz if you prefer a sweeter drink.
Add syrup, lime juice, and gin to a shaker WITHOUT ice, then give it a good swirl so the syrup dissolves. Then add ice and shake vigorously for 5 seconds. Add the club soda last and stir, do not shake.
Strain into a glass over fresh ice and garnish with Thai Basil sprigs. If you like sugar rims, I recommend zesting a lime and finely chopping it into sugar.