I am sure I got the idea from one of the links to her post, but in any case it was extremely tasty and I highly recommend you check it out.
I didn't use the club soda at all, in the end.
3 parts prosecco/sparkling wine
1 part Aperol
splash fresh-squeezed grapefruit juice
I didn't measure when I was pouring, so feel free to do your own proportions! I think it all depends on how sweet the prosecco is.