Line a small tray with parchment paper. Spoon the melted white chocolate into a piping bag or zip-top bag with one corner snipped. Pipe four ghost shapes onto the paper and press two dark chocolate chips into each as eyes. Place the tray in the fridge until the ghosts set firm.

Brew the espresso shots and let them cool for a few minutes so they do not melt the ice too quickly during shaking.

Fill a cocktail shaker halfway with ice. Add the cooled espresso, vodka, and white chocolate liqueur. Secure the lid and shake hard for 15 seconds until the mixture is well chilled and frothy.

Strain the drink evenly into four chilled martini glasses, leaving the foam on top.

Gently lift each set white chocolate ghost from the parchment and rest one on the foam of each glass.