Preheat Oven: Start by preheating your oven to 350°F (175°C). Grease and line an 8-inch round cake pan to help the cake come out easily after baking.
Mix Dry Ingredients: In a large bowl, whisk together the pistachio flour, almond flour, granulated sugar, salt, and baking powder.
Combine Wet Ingredients: In another bowl, whisk the eggs, melted butter, olive oil, vanilla extract, and pistachio extract until well mixed.
Combine Mixtures: Add the wet ingredients to the dry ingredients. Mix until just combined. Be careful not to over mix!
Bake: Pour the batter into the prepared pan. Bake for 25-30 minutes or until a toothpick comes out clean. Let the cake cool completely in the pan.
Prepare Ganache: While the cake cools, heat the heavy cream until it starts to steam. Pour it over the chopped dark chocolate and let it sit for 5 minutes. Then, stir until smooth.
Assemble: Once the cake is cooled, pour the chocolate ganache over the top. Let it dribble down the edges and garnish with slivered pistachios.