Add all ingredients to a tin, seal tightly, and dry shake (The objective here is not only to mix the ingredients but also to aerate so shake as long and hard as you can)
Fill with ice and shake until thoroughly chilled, about 15 seconds (the bottom of a metal shaker should frost over).
Grab a pair of pre-chilled glasses and strain cocktail into both glasses. Garnish with shaved chocolate and conchita if desired and serve.
Notes
Pro Tips
When dry shaking, be sure to hold both parts tightly as the air will expand the mixture.
Practice makes perfect. The secret to aerating (by dry shaking) without getting tired quickly is practice, just as a boxer must spar before a big fight. Repetition over time will yield improved results.
Chill your glassware for a minimum of 30 minutes before you plan to use it, but ideally for a few hours whenever possible.
Wait until the last moment to pull your glassware from the refrigerator or freezer to allow for maximum chill.