How to Make It
In a heatproof medium bowl, whisk the egg yolks with the sugar, cornstarch and salt until well blended.
In a medium saucepan, combine the heavy cream, buttermilk and vanilla and bring to a simmer. While whisking constantly, slowly drizzle 1/4 cup of the hot cream mixture into the egg yolk mixture. Slowly whisk in the remaining cream mixture. Return the pudding to the saucepan and cook over moderately low heat, whisking occasionally, until thickened, about 7 minutes. Scrape the pudding into a medium bowl and whisk in the lemon zest and lemon juice. Press a sheet of plastic wrap directly on the surface of the pudding and let cool to room temperature, about 45 minutes. Refrigerate until cold, about 3 hours.
Swirl the whipped cream into the pudding. Serve in bowls topped with berries.