1- In a nonstick saucepan, combine the condensed milk with the chocolate and 1 tablespoon of butter. Cook over moderately low heat, stirring constantly, until shiny and very thick, 15 to 18 minutes. Spread the mixture in a shallow dish and let cool for 15 minutes, then refrigerate until chilled.
2- Arrange 30 paper candy cups on a baking sheet. Pour the sprinkles into a shallow bow. Rub your hands with butter. Scoop up rounded teaspoons of the candy mixture and roll them into balls. Roll the candy in the sprinkles and set them in a paper cup. Repeat to form the remaining candies. Serve slightly chilled or at room temperature.
You can do Pecan-Cinnamon variation replacing the bittersweet chocolate with white chocolate. In place of sprinkles, blend 1 cup chopped toasted pecans with 1 teaspoon cinnamon and use to coat the candies.