Rhum Agricole is a tasty addition to this cocktail, but your choice of base rum is what will make this Club special. Charles H. Baker specifies "Cuban...
I can't seem to get Clement Rhum Agricole Blanc out here in the provinces nowadays but I did have Rhum J.M Blanc, which is a bit less grassy than Clement, so I upped it to 1/2 oz along with 1.5 oz El Dorado 3-year-old white Demerara rum per F. Yarm's recommendation. This restored Baker's 2 oz of rum, with slightly greater amounts of vermouth (Cocchi) and falernum (J. Taylor). A fascinating, suitably complex but not tiki-grade over-the-top, and harmonious combination of flavors; I never would have thought to combine white Demerara rum, rhum agricole blanc, and dry vermouth in a single drink. Expressed lemon zest seems like the perfect garnish. And it's as crystal-clear as a martini.