Prep the Rim: Dip the rim of a chilled martini glass into chocolate syrup on a plate, then gently press it into crushed pistachios until fully coated. Set aside.
Combine Ingredients: Fill a cocktail shaker halfway with ice. Pour in the cream pistachio liqueur, vodka, and dark crème de cacao.
Shake Vigorously: Seal the shaker tightly and shake hard for 15 to 20 seconds until the outside of the shaker feels frosty.
Strain and Serve: Double-strain the mixture through a fine-mesh strainer into your prepared rimmed glass.
Garnish: Dust top foam lightly with cocoa powder or fresh dark chocolate shavings. Serve cold!