Step 1

Heat the oven to 350°F. Spray 3 8-inch round pans with nonstick spray. Line the bottoms with parchment paper cut into a circle to fit the pan. Spray the parchment paper with nonstick spray and dust the pan lightly with cocoa powder. Tap out any excess and set aside.

Step 2

In a medium bowl, combine the flour, cocoa powder, baking soda, baking powder, and salt. Stir with a whisk and set aside.

Step 3

Add the chocolate to a small heatproof bowl and set it over a pot of barely simmering water. Stir continuously until melted and smooth. Remove from heat. Set aside to cool.

Step 4

Using a stand mixer fitted with a paddle attachment or a handheld electric mixer beat the butter and sugar together on medium-low speed until light and fluffy. Beat in the eggs, one at a time, mixing well after each addition. Scrape down the sides of the bowl as needed. Beat in the vanilla. Add the melted chocolate and mix until well incorporated. With the mixer set to low speed. gradually add half the flour mixture, followed by the buttermilk and coffee, and then the remaining flour mixture. Beat just until combined. The batter will be thick.

Step 5

Divide the batter evenly between the 3 prepared pans. Use an offset spatula to spread the batter all the way to the edges of the pan and smooth out the surface. Bake for 30 to 40 minutes, or until a toothpick inserted into the center comes out with only a few dry crumbs. Cool the cake in the pans for 10 minutes, then invert the cakes onto a wire rack to cool completely. Peel the parchment paper off the bottoms before filling.

Step 6

In a food processor, process the pistachios until they become coarsely ground. Stop and scrape down the sides of the bowl. Add the oil if the pistachios aren't breaking down easily. Continue to blend for 25-30 minutes, stopping and scraping down the sides as needed throughout the process until smooth and creamy. Set aside.

Step 7

In a stand mixer fitted with a paddle attachment or with an electric hand mixer, beat the butter on medium-high speed until smooth. Add the cream, vanilla, and salt. Continue to beat until incorporated.

Step 8

Add 2 cups of confectioner's sugar, beat on medium-low speed until most of the sugar is moistened. Gradually add in the remaining sugar, one cup at a time. You may need more or less depending on how soft the butter is. Beat on medium-low speed until the sugar is moistened. Turn the speed up to medium-high and beat until light and fluffy. Scrape down the sides of the bowl as needed. Add the pistachio paste and food coloring. Mix until well combined.

Step 9

Place one cake layer onto a serving platter. Add a generous amount of frosting and spread it to the edge with a spatula. Repeat with a second cake layer, topping it with a generous amount of frosting. Add the third cake layer and cover the top and sides of the cake with frosting. Press chopped pistachios into the sides of the cake near the bottom and coming up less than halfway. Sprinkle pistachios over the outer edge on top of the cake creating a 1-inch border. Set the cake in the freezer for 10 minutes.

Step 10

Place the chocolate, butter, and corn syrup in a medium heatproof bowl set over a pot of barely simmering water. Stir until melted and smooth. Remove from heat and let cool for 5 minutes.

Step 11

Spoon the ganache over the top of the cake in the center of the pistachio border. Use the back of the spoon to create a smooth layer of ganache. Set the cake back into the freezer for 10 minutes.