Preheat your oven to 350°F (175°C). Grease two 9-inch round cake pans and line the bottoms with parchment paper to ensure easy release.
In a large bowl, sift together the all-purpose flour, black cocoa powder, granulated sugar, baking soda, baking powder, and salt. Whisk until well combined.
In another bowl, whisk the vegetable oil, buttermilk, eggs, and vanilla extract until smooth and homogenous.
Gradually add the wet ingredients to the dry, mixing gently with a spatula or whisk until just combined. Avoid overmixing to keep the cake tender.
Carefully pour the boiling water into the batter and stir gently. The batter will be thin – this is expected and ensures a moist, rich cake.
Divide the batter evenly between the two prepared pans. Bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs.
Allow the cakes to cool in the pans for 10 minutes, then turn out onto cooling racks. Let them cool completely before frosting.
Spread a generous layer of chocolate frosting between the two cake layers and over the top and sides. To create the cobweb effect, pipe concentric circles of decorative frosting on top, then drag a toothpick from the center outward to form the web pattern.
