The Cocktail Book a Sideboard Manual for Gentlemen (1901, p.34)

1 dashAbsinthe base
0.67 portionWhiskey — Source gives two-thirds.base
0.33 portionItalian vermouth — Source gives one-third.modifier
  1. Fill a mixing glass with ice and add the ingredients.
  2. Mix and strain into a cocktail glass.

Ice: Ice

This is a very useful transitional aromatic because it drops bitters entirely while still living firmly inside the whiskey-vermouth field.

The explicit 'No bitters' note is the defining differentiator.

See also: Manhattan Cocktail, Martini Cocktail

Source explicitly says 'No bitters.'