1In 2-quart heavy saucepan, heat 2 cups of the milk to boiling. Remove from heat; add dark chocolate, stirring with wire whisk until smooth. Set aside.
2In small bowl, mix granulated sugar, cocoa, cornstarch and cinnamon. Stir in remaining 1/4 cup milk. Add cocoa mixture to melted chocolate mixture in saucepan, beating until well blended. Heat to boiling over medium heat, stirring constantly. Reduce heat; simmer 1 minute. Remove from heat.
3In medium bowl, beat eggs with wire whisk. Slowly beat in about 1 cup chocolate mixture. Add to remaining chocolate mixture in saucepan; cook over medium heat, stirring constantly, until mixture thickens and boils. Remove from heat; stir in butter and vanilla. Transfer pudding to large bowl. Cool 15 minutes. Cover top of pudding with plastic wrap to prevent skin from forming. Refrigerate 2 hours or until chilled.
4In medium bowl, beat whipping cream, powdered sugar and food color with electric mixer on medium speed until soft peaks form. Remove pudding from refrigerator. Beat pudding until smooth. With rubber spatula, fold whipped cream mixture into pudding for swirled effect. Serve or refrigerate.