Preheat your oven to 350 degrees, and grease three 8-inch round cake pans. Set aside. 

In a large bowl, or the bowl of a stand mixer, stir together the ground pistachios, cake flour, baking powder, baking soda, salt, and sugar. Beat in the softened butter until completely combined, several minutes. The mixture should be crumbly and slightly yellow in color from the butter. 

In a medium bowl, whisk together the oil, eggs, sour cream, vanilla extract, and buttermilk. Add the wet mixture into the dry in three parts, mixing well between each addition. Beat for several minutes after all the liquid has been added until the batter is well mixed, and slightly lighter in color. 

Spread evenly in your prepared pans, and bake for 30-35 minutes, or until a cake tester comes out clean. Cool completely before removing from pans and frosting. 

In a large bowl, beat the butter and cream cheese together until combined. Add in the powdered sugar, cocoa powder, and salt, and beat until completely combined and smooth. Add in the melted chocolate, beating until combined. Then add in the heavy cream, and whip for several minutes until fluffy. Frost the cake as desired!