In a saucepan heat heavy cream, vanilla bean and salt and bring to a gentle boil. Meanwhile, in bowl of an electric mixer set over a pan of simmering water melt chocolate, stirring often, until smooth. Remove chocolate from heat. Strain cream mixture through a fine sieve into chocolate. (Rinse vanilla beans, dry them and reserve for vanilla sugar or another use.) Replace bowl in electric mixer and whip chocolate ganache mixture until cool and light in color. Cover and chill.
When ganache is firm, spoon up about 1 tablespoon. Place cocoa in a shallow plate and use to dust palms. Lightly and quickly roll chocolate mixture between palms to form irregularly-shaped balls. Dredge truffles in cocoa until well-coated. Set on a foil-lined baking sheet while you continue to make truffles with remaining ganache. Best when served within 24 hours, or store in a cool place up to 3 days.