Place chopped chocolate in a large heatproof bowl.
Place cream into a medium saucepan. Cook over med heat, stirring often, until it just barely starts to simmer.
Pour hot cream over chopped chocolate and cover bowl with plastic wrap. Let sit 5 minutes.
Stir gently with a spatula until completely smooth. Add softened butter and stir until smooth. If needed, place over a double boiler and stir until all chocolate and butter has melted.
Place plastic wrap directly on top of chocolate ganache. Allow to thicken and set overnight.**
Preheat oven to 350F. Grease and flour three 6" cake rounds and line with parchment.
In a medium bowl, whisk flour, ground pistachios, baking powder,and salt until well combined. Set aside.
Using a stand mixer fitted with a paddle attachment, cream butter and sugar on med-high until pale and fluffy (approx 3mins). Reduce speed and add eggs one at a time fully incorporating after each addition. Add vanilla.
Alternate adding flour mixture and milk, beginning and ending with flour (3 additions of flour and 2 of milk). Fully incorporating after each addition.
Bake for approx. 35-40mins or until a toothpick inserted into the center comes out mostly clean.
Place cakes on wire rack to cool for 10mins then turn out onto wire rack. Allow cakes to cool completely.
Place one layer of cake on a cake stand or serving plate. Top with approx 2/3 cup of thickened ganache, spread evenly. Press cut raspberries into the ganache (I used about 12 halves per layer) and sprinkle with finely chopped pistachios (about 1 Tbsp). Repeat with next layer.
Place last layer on top and smooth the outside with a thin crumb coat. Let sit at room temperature for 20mins. The ganache on the cake will firm up slightly.
Frost the top and sides of the cake with the remaining ganache. Do a swirl on top and use a decorative scraper to do the sides. I used the far left one pictured here.
Press chopped pistachios into the bottom and sprinkle some more on top of the cake. Decorate with raspberries if desired.
* Pulse 1 cup of shelled, unsalted pistachios in a food processor until they are fine and powdery. Pass through a sifter and measure out 3/4 cup. Reserve remainder for sprinkling between layers. ** You can speed up the thickening of the ganache by placing the it in the fridge, but you need to stir it often.