Arrange two shallow dishes on a flat surface. To the first, add chocolate syrup in a circular pattern approximately the size of the rim of the glass. To the second, pour the crushed cracker crumbs.
Swirl the rim of a chilled martini glass in the chocolate syrup, then immediately dredge in graham cracker crumbs. Set aside.
Fill a martini shaker with ice. Add chocolate liqueur, crème de cacao, and vodka. Shake vigorously until chilled, about 20 seconds. Strain into the prepared glass and garnish with a marshmallow. Serve immediately.
Yield: The recipe as written makes one delicious, chocolatey cocktail.
Big batch: To make a large batch of 8 cocktails, in a large pitcher combine 2 cups chocolate liqueur, 1 cup crème de cacao, and 1 cup vodka. Chill until serving time. Follow the instructions for rimming the glasses with chocolate and graham cracker crumbs. Set out the pitcher of martini mix and 8 glasses with mini marshmallows on the side for garnish.