Using tip of small knife, scrape seeds from vanilla bean into processor; reserve bean. Add sugar to processor and blend 10 seconds. Transfer 3 tablespoons vanilla sugar to small bowl and reserve.
Transfer remaining vanilla sugar from processor to heavy medium saucepan. Add unsweetened cocoa powder, 1/2 cup water and salt and whisk until smooth. Whisk over medium heat just until beginning to bubble. Whisk in whole milk and half and half. Add reserved vanilla bean; bring mixture to simmer. Remove from heat; whisk in vanilla extract. Discard vanilla bean.
Beat cream and reserved 3 tablespoons vanilla sugar in medium bowl until medium-firm peaks form. Divide hot chocolate among 6 mugs; top with whipped cream and serve.
