Swipe the rim of a martini glass with a little water and rotate it through the shaved chocolate.
In a cocktail shaker, muddle the mint leaves and vanilla bean seeds together and top with ice.
Add the heavy cream, crème de cacao and crème de menthe and shake for 30 seconds.
Strain the cocktail into the martini glass and garnish with a little more shaved chocolate and a mint leaf. Serve immediately.