Alexander
1 1/2 ounces brandy
1 ounce cream
1 ounce crème de cacao
Garnish: Sprinkle of nutmeg
Shake with ice. Strain into a cocktail glass.

Also often referred to as a “Brandy Alexander”, which suggest you could use other spirits in place of brandy. When faced with the constant request for a “Chocolate Martini” it can usually work to serve this and let folks know it was perhaps the “original”.