I feel like this, much like the Edison's medicinal cocktail, can be served dumped with some additional ice. The additional basil helps lift the gin and the freshness from the slightly-too-sweet cocktail is otherwise.
I cut down the quantities to bring std drink measure down. 45 ml gin, 22.5 ml elderflower etc.
Lovely drink for upping the G&T game. Still a little sweet with the elderflower- probably up the gin and lower the elderflower next time 50-20.
Tried this with just 2 medium sized basil leaves (usual UK supermarket type!). Their flavour marries perfectly with the celery gin, not too forward. Also used Fever Tree Light which helps retain the lemon tartness of the juice. This is a real winner and a superb take on a regular G+T.
I would suggest spicy bush basil for those who find the regular basil too much. Also, if your basil is too bitter, a little splash of Midori goes nicely in this drink.