Preheat oven to 350° F. Grease and flour a 9-inch square baking pan, and set aside. Throw the 1½ cups shelled pistachios into a food processor or blender, with a splash of water. Purée until it forms a thick paste, set aside.

Make the cake: In a large bowl, whisk together the flour, baking soda and salt; set to the side. In a separate bowl, beat together the butter and sugar until light and fluffy. Add in the eggs, one by one, mixing well after each addition. Stir in the vanilla extract and half of the pistachio paste. Add the dry ingredients alternately with the buttermilk, starting and ending with the dry ingredients. Stir until just combined. Pour the batter into the prepared pan and bake for about 20 to 25 minutes or until a toothpick inserted in the middle, comes out clean. Let cool for about 15 minutes, before inverting onto a wire rack and cooling down completely.

To make the pastry cream: Whisk together the sugar, cornstarch, salt and vanilla seeds (scraped from the vanilla bean) in a small sauce pot. Stir in the milk and egg yolks and whisk until smooth. Cook over medium heat, stirring constantly until it has thickened, about 10 minutes. Remove from heat and add the butter, vanilla and remaining half of pistachio paste. Stir until well incorporated. Transfer to a heatproof bowl and cover with plastic wrap, making sure the wrap touches the cream directly. Chill in the fridge until firm, about 2 hours, or overnight.

To make the glaze: Bring the cream to a simmer in a small pot. Place the chocolate in a small bowl and pour in the hot cream. Allow to sit for about 5 minutes without stirring. Stir until the chocolate has fully melted and is glossy.

To assemble the cakes, cut the cooled cake into quarters (four even squares). Using a 4 inch round cookie cutter, cut each cake square into a circle. Eat the scraps. That's important. Cut each circle in half so you end up with two thin layers for each. Spread half of the circles with the chilled pistachio pastry cream, top with the remaining cake layers. Place in the freezer and allow to chill for about 5 minutes to speed up the firming process. Spread the melted chocolate on top of each and sprinkle with chopped pistachios. Store in the fridge until ready to serve. Enjoy!