Place four martini glasses in the refrigerator to chill for at least 30 minutes.
Fill a cocktail shaker about halfway with crushed ice. Add white chocolate liqueur, crème de cacao, vanilla vodka, and half-and-half to the shaker.
Secure the lid tightly and shake vigorously for about 30 seconds, until the mixture is well chilled.
Strain the mixture evenly into the chilled martini glasses.
Garnish each glass with dark chocolate shavings.
Serve immediately while cold.