Place the heavy cream and sugar in a medium saucepan over medium-high heat. Cut the vanilla bean in half lengthwise, and scrape the seeds into the heavy cream. Add the cut vanilla bean to the cream. Bring the mixture to just a boil, and turn off heat. Cover pot, and let steep for 30 minutes.
Sprinkle unflavored gelatin over 1/2 cup cold water in a small bowl. Let the gelatin bloom while the heavy cream mixture is steeping.
Bring heavy cream mixture back to a simmer, and slowly whisk in melted gelatin mixture. Add buttermilk, and whisk until combined.
Pour into individual glasses or bowls, and gently cover with plastic wrap. Chill for about 3 hours or overnight; serve.