In a small saucepan, combine the sugar, water, and kosher salt. Bring to a boil, then reduce heat and simmer until liquid has reduced by about 1/3. You should have 12-16 oz by the end. Remove from heat, add the vanilla and basil sprigs and stir. Steep the sprigs for 3-5 minutes until wilted, then remove. Transfer to a bottle and store in the refrigerator.
For mixed drinks, use about 1 tsp per 8 oz of liquid. Serve with fresh citrus and sparkling water, or develop your own mixed drink creation!