- In a medium saucepan cook and stir bittersweet chocolate over low heat until melted. Gradually whisk in milk. Meanwhile, in a small bowl stir together sugar, cornstarch, cocoa powder, and salt. Whisk sugar mixture into chocolate mixture.
- Cook and stir over medium heat until thickened and bubbly. Cook and stir for 2 minutes more. Stir in vanilla. Remove from heat; cool for 45 minutes. Whisk mixture until smooth.
- Spoon mixture into nine 3-ounce frozen pop molds.* Add sticks; cover and freeze for 3 to 4 hours or until firm. Let stand for 10 minutes before unmolding. If desired, dip pops in melted white chocolate and chocolate pieces, and/or dip in melted dark chocolate and shortbread cookies.
If frozen pop molds are unavailable, use 3-ounce wax-lined paper cups instead. Spoon chocolate mixture into cups; cover each top with a piece of foil. Using a small sharp knife, make a slit in each piece of foil. Insert wooden pop sticks into slits. Freeze and serve as directed.