Wayne Collins, this drink's creator, originally used equal parts as is usual for a classic Negroni and after trying various other formulations, I've found...
Following the discussion with Chris brislawn on these pages, if you sub half the Lillet for Bonal or another available Kina you’ll get something much more pleasingly adult and bittersweet. On this occasion I went with Sipsmith 30, Suze 30 (haven’t been able to source salers for comparison) 15 each Lillet and bonal. Very satisfying digestif.
Just escaped a bitter Midwest blizzard while on travel, made it home tonight and was told to come up with a cocktail to celebrate our safe return. I'd been wanting to try a new bottle of Suze (my first) and decided a White Negroni sounded appropriate to the occasion. When I pulled up the classic Wayne Collins recipe in Difford's Guide I saw that Discerning Drinkers had recently been deconstructing it, and John Carr's idea of splitting the Lillet Blanc with another bitter white aperitif appealed. I made 2 versions, both using 1 oz Bombay Sapphire, 1 oz Suze and 1/2 oz Lillet Blanc, and 1/2 oz of either Bonal Gentiane-Quina or Luxardo Bitter Bianco. The color is unfortunate, the Bonal version in particular resembling a sample one's physician might send off to the lab for diagnostic tests, but we were not deterred. The Luxardo version was brighter in both color and flavor---both a bit sweeter and a tad more bitter---while the Bonal version had richer, more complex, more vegetal flavors; "artichoke" was mentioned, although I don't know if Bonal contains any. Both are interesting in their own rights. Lots of room for experimentation.