Great recipe! Grapefruit twist is ideal but I made one with lemon too and that worked.
I make another drink that has an identical build but uses Cointreau (in place of Elderflower) and absinthe (in place of celery bitters) with an orange twist. I've heard it called a Foghorn, but there's a better known drink by that name as well. Reccomend checking that out if you like this!