For a sweeter variation, substitute 12 ounces milk chocolate for the bittersweet chocolate. You can make this pudding several days ahead and then assemble in teacups or wineglasses with whipped cream up to two hours in advance.* Serve with warm Peanut, Coconut, and Chocolate Cookies.
Whisk together first 3 ingredients in a medium bowl until blended.
Combine milk and 1 cup cream in medium saucepan, and cook over medium heat until hot. Gradually pour hot milk mixture into egg mixture, whisking constantly. Return mixture to saucepan, and cook over medium-low heat, stirring constantly with a heat-resistant spatula, for 5 minutes or until mixture thickens and coats the spatula or until candy thermometer reads 180°.
Remove saucepan from heat. Add chocolate, and let stand 10 seconds; whisk until smooth. Transfer chocolate cream to a clean bowl. Place plastic wrap directly on the surface of the cream, and refrigerate until cold and set, at least 3 hours.
Combine remaining 1/2 cup cream, sugar, and vanilla in a medium bowl. Beat at high speed with an electric mixer until soft peaks form. (Do not overbeat.) Dollop onto each serving of pudding.
*Serving suggestion: Divide half the whipped cream evenly among six wineglasses. Spoon about 2/3 cup chocolate pudding over the cream in each glass, and top with remaining whipped cream.