Bake cake in 9- by 13-inch pan according to directions on box.
Once cake has baked and cooled, crumble entire cake into a large bowl. Add 2/3 of the frosting, and mix the cake and frosting with your hands. Roll into balls a little smaller than a golf ball. Lay on cookie sheet lined with wax paper, and freeze for at least 2 hours.
Once cake balls are frozen, dip in melted white chocolate and return to cookie sheet. Then drizzle the melted milk chocolate over the cake balls for a decorative touch.