Black Cake

1. Preheat your oven to 350°F. Grease and line an 8×3-inch pan, or two 8×2-inch pans, with baking spray and a round of parchment paper cut to fit the bottom.
2. In a large mixing bowl, whisk together the cake flour, black cocoa powder, baking powder, and fine sea salt until the dry ingredients are evenly distributed with no visible streaks of cocoa or salt.
3. In a separate large bowl, whisk together the granulated sugar, neutral oil, room-temperature eggs, and sour cream until the mixture looks smooth, well combined, and slightly thickened.
4. Sift the dry ingredient mixture directly over the wet ingredients and whisk them together only about halfway — you’re looking for a rough, partially combined batter at this stage rather than a fully smooth one.
5. Pour in the hot coffee and whisk the entire mixture until the batter turns completely smooth, with every trace of the dry ingredients fully incorporated.
6. Scrape down the edges and bottom of the bowl with a spatula and give the batter one final thorough mix to make sure nothing is hiding unmixed at the bottom. Pour the batter evenly into your prepared cake pan or pans.
7. Bake for approximately 40 minutes, checking doneness by gently pressing the tallest part of the cake in the center — it should spring back fully when it’s ready. If it feels soft or leaves an indent, give it another minute or two in the oven before testing again.
8. Let the cake rest in its pan for about 10 minutes once out of the oven. Then, carefully flip it out onto a clean tea towel and let it cool upside down for around 30 minutes before flipping it back over the right way.
9. Once the cake has cooled completely, slice it horizontally into two even layers using a long serrated knife.

Espresso Syrup

10. In a small bowl, stir together the espresso, honey, and ground cinnamon until fully combined into a smooth syrup. Let it cool for a few minutes so it isn’t hot when it touches the cake.
11. Using a pastry brush or a spoon, brush or drizzle half of the espresso syrup evenly over the cut, exposed side of each cake layer, letting it soak in before moving on to frosting.

Pistachio Cream

12. In the bowl of a stand mixer fitted with the whisk attachment (or in a large bowl using a hand mixer), beat the cold mascarpone together with the powdered sugar until the mixture turns completely smooth with no lumps remaining.
13. Add the vanilla bean paste to the bowl and turn the mixer to medium speed, mixing just until it’s incorporated.
14. With the mixer still running on medium, slowly stream in the cold heavy whipping cream in three to four separate additions, stopping between each pour to scrape down the sides and bottom of the bowl with a spatula.
15. Once all of the heavy cream has been added, the mixture may look soft and loose at first. Turn the mixer up to full speed and continue beating — within a couple of minutes, it should thicken noticeably and begin holding firm peaks. Watch it closely at this stage and stop mixing as soon as it reaches that point, since overbeating can cause the mixture to turn grainy or split.
16. Add the pistachio butter or paste to the whipped mixture (pressing it through a fine sieve beforehand if you’d prefer a completely smooth cream without any chunks), along with the tiny pinch of fine sea salt. Mix on low speed just until everything is evenly combined — avoid overmixing at this stage as well.

Assembly

17. Place the bottom cake layer, soaked side up, on your serving plate or cake stand. Spread half of the pistachio mascarpone cream evenly over the top in a smooth, even layer.
18. Warm a small amount of extra pistachio butter or paste in the microwave for a few seconds until it loosens into a pourable consistency, then drizzle it generously over the mascarpone cream layer.
19. Place the second cake layer on top, soaked side down, and press down gently to help it settle. Spread the remaining pistachio mascarpone cream over the top layer, then finish with another drizzle of warmed pistachio butter or paste. Top with chopped pistachios, if desired, before slicing and serving.