Add basil to the bottom of a cocktail shaker then gently muddle until the leaves start to release their juices. Add lime juice, maple syrup, and herbal simple syrup to the cocktail shaker then muddle until you’ve extracted all the liquid from the basil leaves. Finally, add in the gin, grapefruit bitters, and several ice cubes then place the lid on the cocktail shaker and shake until it becomes cold, about 1 minute.