Basically, a Negroni with bourbon replacing gin. The original 1927 recipe calls for equal parts, but I've previously favoured a 3:2:2 (45ml bourbon, 30ml...
I made this with the 2:1:1 and also tried the original equal parts. In the 2:1:1 I have to say Eugene has hit the nail on the head as the bourbon does indeed define the drink. In all honesty I found it to be a nicely balanced bourbon forward drink where the vermouth and the red bitter liqueur act more like exotic bitters than as negroni ingredients. For me I prefer the original equal parts but there's no denying the balance in the 2:1:1 is sublime.