Alexander I was made with gin. Because that spirit was scarce in the ’40s, rum and brandy were often used as substitutes in cocktails—not always to great effect. This is one case where the derivation more than equals the original, though using a less-sweet brandy helps keep the cocktail from edging into the realm of cloying. A pony is a one-ounce shot glass.
In a mixing glass combine 1 pony brandy, 1 pony heavy sweet cream, and 3/4 pony crème de cacao. Shake well and fast with cracked ice, not cubes, and strain into a chilled cocktail glass.
