• 20 ml Fernet Branca
• 20 ml herbal liquor (or green chartreuse if you can find it)
• 20 ml lime juice
• 10 ml simple syrup
• 10 ml Aquafaba

Shake everything well, and serve.
I'm going with metrics measurements now, so I don't have to convert them ^^

A really interesting combination of flavors, the mint from the Fernet Branca is still there, but more of an aftertaste. I can see it being better balanced with the chartreuse, since it is higher abv.

I think I've got all this on hand...

I've always seen this as an equal parts formula. Is that 50/50 simple? I need to try it with Aquafaba. That probably adds some welcome viscosity.

Looks nice. Does aquafaba also require dry shaking, like eggs do?

It's 1.5 part sugar to 1 part water.
I'm using the Difford's recipe: https://www.diffordsguide.com/cocktails/recipe/25001/industry-sour
But I can see different ratios working, both the Fernet and the liquor are strong flavors!

I do reverse dry shaking (first with ice, then without), as I don't get good results otherwise. But aquafaba is not as reliable as eggs white I would say, it depends on how you get it, and which brand of chickpeas.
I use it because I do hummus a lot, so get the aquafaba "for free" :)