Gary Regan, in his book Joy of Mixology, adapted the original 1930s recipe by substituting Amaretto for Crème de Noyau and dropped the Orange Bitters. He, of course, tweaked with the ratios a bit but thankfully kept the Gin, lemon Juice and Angostura Bitters.
Shake with ice and fine strain into a chilled cocktail glass.
Orange zest twist