For the Pudding: Bring to a boil the milk and vanilla bean in a large heavy bottomed pot.
Meanwhile, whisk to blend the eggs, egg yolks, potato starch, sugar, cocoa powder, and flour. Remove the milk pan from heat once it boils. With the whisk in the center of the cocoa mixture, slowly pour the hot milk in and begin to combine the 2 mixtures. Finish pouring the milk in and whisk to fully incorporate.
Return mixture to the pot and cook over medium heat, slowly whisking constantly to prevent scorching. The ingredients have a low burning temperature and will scorch easily so keep the whisk moving. Cook until large bubbles slowly rise to the surface of the pot. I call these "lava bubbles" because the large steam venting bubbles make me think of flowing molten lava. The pastry cream temperature is approximately 200 degrees F. Remove pot from the heat and whisk in the butter. Remove the vanilla bean from the pudding. Pour pudding into a heat resistant bowl and cover with plastic wrap, making sure the plastic wrap touches the surface of the pudding to prevent a skin from forming.
For the Whipped Cream: Combine all the ingredients in a mixer bowl and whip on medium speed. Stop the mixer when you have medium peaks and finish whipping manually with whisk. This will help avoid ruining the whipped cream's luscious texture.
For the Raspberry Puree: Combine the frozen berries and sugar in a pot and bring to a gentle simmer. Cook gently for 5 minutes. Strain the berries to remove the seeds. It's easier to pour if you can put it in a squeeze bottle.
Ganache: Bring the heavy cream to a boil and immediately pour over the chocolate. Stir to combine. Allow to cool for easy handling.
Berries: use the freshest and plumpest berries available.
Assembly: Load pudding and whipped cream into separate pastry bags. Alternately pipe into tall sundae glasses, starting with chocolate pudding, then the whipped cream, rapsberry puree and fresh berries. Repeat as needed and top the parfait with whipped cream and fresh berries. Drizzle chocolate ganache across the top for extra indulgence!