Make ahead: Prepare the martini mixture up to 5 days in advance and refrigerate an airtight container. Shake with ice before serving.
To serve a crowd: You can scale up the recipe and mix ingredients in a pitcher. Shake in small batches as needed.
Ingredient variations: If you don’t want to invest in both chocolate liqueur and Baileys, swap the Baileys with more chocolate liqueur and add 1 ounce half-and-half.