Rim a chilled martini glass with cocoa powder or finely grated chocolate by moistening the rim with a thin layer of simple syrup or espresso, then dipping it into the cocoa powder.

In a shaker, combine vodka, chocolate liqueur, creme de cacao, espresso or coffee liqueur, and simple syrup.

Add a generous handful of ice and shake vigorously for about 15 seconds until well chilled and frothy.

Strain into the prepared glass through a fine mesh to ensure a smooth finish.

Garnish with chocolate shavings or a light dusting of cocoa powder.