Dip the rim of a chilled martini glass in water (or melted chocolate if you want to be fancier) and then directly into the cacao powder.
In a cocktail shaker, add ice then top with the vanilla vodka, crème de cacao and chocolate liqueur. Shake until frosty, and pour into the chilled martini glass. Add heavy cream to cut the alcohol if desired.
Garnish: Stick a skewer into the tip of a strawberry to stand it up on its base. Cut little petals around the base of the strawberry (not cutting all the way to the bottom) and continue this process up to the tip of the strawberry until it looks like a rose. Slide onto a long toothpick and insert into the martini glass.