In doing some research on the Hoffman House cocktail, it seems as though the original recipe called for Holland gin (genever), Italian (rosso) vermouth and Boonekamp-style bitters (e.g. Underberg).

18 September 1892, New York (NY) Herald, “Appetizing Drinks,” pg. 14, col. 6:
Mr. William Henry Dugay, or “Billy,” as he is known to his intimates, has been one of the “star” bartenders of the Hoffman House for about ten years, and yesterday he let a HERALD reporter into the secret if the great success attending some of his choicest mixtures. He said:—

“The Hoffman House cocktail is a favorite morning beverage with the regular patrons of the hostelry and with no one more so than Mr. Stokes, the proprietor. It is simply made and therefore highly recommended for home manufacture. This is the recipe:—Two dashes of Bonecamp bitters, two dashes of Italian vermouth, sherry glass of Holland gin” no sweetening. Stir in ice until very cold.”