Jörg, the creator of this cocktail, says, "Better too much than not enough basil in this drink". He also specifies that the basil is muddled rather than...
As with pesto alla genovese you have to really mash the hell out of fresh, springy basil to get the oil out of the plant and onto your tongue. I also put the gin and lemon juice in and a quick stir before adding the ice. Tasted amazing.