Bring whipping cream to simmer in heavy medium saucepan. Whisk egg yolks and sugar in medium bowl to blend. Gradually whisk hot cream into egg yolk mixture. Return mixture to saucepan and stir over medium heat until custard thickens slightly, about 6 minutes (do not boil). Strain into bowl. Stir in 1 cup cold buttermilk. Refrigerate custard until cold, about 2 hours. Process in ice cream maker according to manufacturer's instructions. DO AHEAD Can be prepared up to 5 days ahead. Freeze in covered container.