1. Preheat the oven to 350°F. Grease a 9-inch round baking pan and line the bottom with parchment paper.

2. In a large bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt.

3. In a separate bowl, beat the eggs, milk, oil, and vanilla until well combined.

4. Gradually add the wet ingredients to the dry ingredients, mixing until just combined. Fold in 1/2 cup of the chopped pistachios.

5. Pour the batter into the prepared pan and bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.

6. Allow the cake to cool completely in the pan, then invert onto a serving plate.

7. In a small saucepan, heat the heavy cream over medium heat until just simmering. Remove from heat and stir in the chopped chocolate until smooth and glossy. Pour the ganache over the top of the cake, allowing it to drip down the sides.

8. Sprinkle the remaining 1/2 cup of chopped pistachios over the top of the cake.

9. Refrigerate the cake for at least 2 hours before serving to allow the ganache to set.