• Preheat oven to 350 degrees F. Grease and flour 2 8-inch round pans.
• Whisk the sifted flour with the baking powder , baking soda and salt; set aside.
• Beat softened butter and sugar in bowl of a stand mixer until light in color, about 2 minutes. Beat in eggs, one by one, and vanilla. Add flour mixture in 3 parts, alternating with buttermilk, beating well after each addition. Pour batter into pans dividing evenly. If you have a scale you can put each pan on it, set tare to "0" and add 18 oz batter.
• Bake until wooden pick inserted in center comes out clean, about 30-35 minutes. The two cakes will most likely bake up flat almost like pound cakes. This is actually helpful because you don't have to trim the domes. Let cool in the pans for about 15 minutes, then carefully invert.

Pastry Cream Filling

• In a saucepan, heat the milk and vanilla bean (split and scrape) until simmering. If using vanilla paste, just heat the milk.
• While milk is heating, whisk the sugar, cornstarch, salt, egg yolks and egg together in a medium size bowl, preferably one with a spout.
• Once the milk is infused with vanilla, remove the bean and pour half of the hot milk over the egg mixture, stirring or whisking until smooth.
• Pour the egg mixture back into the saucepan and whisk constantly over medium low heat until mixture thickens, about 2 minutes. It may take longer, so just whisk until it is as thick as pudding and big bubbles break the surface. Once that happens continue whisking for another 30 seconds.
• Pour the mixture through a sieve set over a clean bowl, then whisk in the butter and vanilla paste (if using). If you used a vanilla bean, taste test and add a little vanilla extract or paste if needed.
• Let cool slightly, then cover directly with plastic wrap to keep a skin from forming. Cool and chill.

Chocolate Glaze

• Combine the chocolate and water (or coffee) in a double boiler or heat proof bowl set over barely simmering water. Heat until melted and smooth. Remove from heat. Add salt, then stir in the butter, 2 pieces at at time. Let cool (I let it cool for about an hour), stirring often, until it is a pourable consistency
• Assemble: Place 1 cake layer on serving plate. Spread with thick layer of pastry cream. Top with second cake layer. Pour glaze over the top and let it drip down the sides. Chill until ready to serve.