Shake all ingredients over ice. Then strain contents out into an empty container. Discard the ice from your shaker. Pour your cocktail back into the shaker and shake again without ice; this is called a “dry shake.” (The dry shake will create a beautiful creamy body and thick pillow on top. You should be able to feel the cocktail “set up” in the shaker with your hand as you shake.) Strain into a chilled martini glass. Top with grated or shaved chocolate or cocoa powder.