1/2 vanilla bean, split lengthwise
1/2 cup sugar
5 cups milk
4 ounces bittersweet (not unsweetened) or semisweet chocolate, chopped
1/4 cup powdered sugar
2 teaspoons unsweetened cocoa powder
1 teaspoon vanilla extract
1/2 cup chilled whipping cream
1. Using small sharp knife, scrape seeds from vanilla bean into small bowl; reserve bean. Add 1/2 cup sugar to seeds; rub with fingertips to distribute seeds. Set aside.
2. Heat 4 1/2 cups milk and scraped vanilla bean in large saucepan over medium heat until hot. Mix in chopped chocolate and 1/3 cup vanilla sugar. Whisk until chocolate melts and mixture is smooth. Mix 1/2 cup milk, powdered sugar, and cocoa in small bowl. Stir into hot chocolate. Bring just to simmer, whisking often. Remove from heat and stir in vanilla extract.
3. Using electric mixer, beat cream and remaining vanilla sugar in medium bowl to soft peaks. Divide hot chocolate among 6 mugs. Top each with whipped cream.