Preheat oven to 350°F (175°C). Grease and line two 8-inch round cake pans with parchment paper.

In a large bowl, whisk together flour, black cocoa, regular cocoa, baking powder, baking soda, and salt. Set aside.

In a stand mixer, cream together softened butter and sugar until light and fluffy, about 3–5 minutes.

Add eggs one at a time, beating after each addition. Mix in vanilla extract.

In a separate cup, stir together blackberry puree, buttermilk, and oil.

Gradually add dry ingredients to the wet mixture, alternating with the blackberry liquid. Mix just until combined.

If desired, add a few drops of red or purple food coloring for a deeper hue.

Divide the batter evenly between prepared pans. Bake for 25–30 minutes, or until a toothpick inserted in the center comes out clean.

Cool completely in pans, then remove and set on a wire rack.

In a medium saucepan, combine blackberries, sugar, lemon juice, and cinnamon stick over medium heat. Simmer for 5–7 minutes, stirring occasionally, until the berries release their juices and begin to break down.

In a small bowl, whisk cornstarch with 2 tbsp water to create a slurry. Stir the slurry into the berry mixture and cook until thickened. Remove from heat and let cool completely. Strain if a seedless filling is desired.

Heat heavy cream in a saucepan over medium heat just until it begins to simmer. Do not boil.

Pour hot cream over chopped chocolate in a heatproof bowl. Let sit for 2–3 minutes. Stir until fully smooth. Add butter (optional) for extra shine. Let ganache cool slightly until it thickens but is still pourable.

Trim domed tops off cake layers if needed for an even surface. Place one cake layer on a cake stand or serving plate.

Spread a thin layer of ganache on top. Add a generous layer of blackberry filling. Top with second cake layer.

Pour ganache over the top, allowing it to drip down the sides for a gothic 'drip' effect.

Garnish with fresh blackberries, black sugar pearls, or chocolate skulls for dramatic flair. Let ganache set for 20–30 minutes before slicing. Slice and serve with red wine or espresso for the ultimate experience.