First, rim the glasses. Begin with two shallow dishes or plates. To one, add a teaspoon of frosting or melted chocolate. To the other, add the sprinkles. Rim the edge of the martini glass first in the frosting and then in the sprinkles. Set aside.
Fill a cocktail shaker with ice. Add the vodka, white chocolate liqueur, amaretto, and half & half. Cover and give the mixture a good shake to combine.