First encountered in Jerry Thomas' 1887 Bartender's Guide, he specifically notes that "The name of this cocktail is a misnomer, as coffee and bitters are not to be found among its ingredients, but it looks like coffee when it has been properly concocted, and hence probably its name."
1 1/2 oz port
1 1/2 oz brandy
1 tsp. simple syrup
1 whole egg
dash Angostura Aromatic Bitters
Dry shake (no ice), add ice and shake.
Strain into a wine glass.
Garnish with grated nutmeg.