Follow these straightforward steps to create your Blackberry Velvet Gothic Cake:

1. Preheat Oven: Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

2. Mix Dry Ingredients: In a large mixing bowl, sift together the flour, granulated sugar, cocoa powder, baking soda, baking powder, and salt.

3. Combine Wet Ingredients: In another bowl, whisk together the buttermilk, vegetable oil, eggs, vanilla extract, and blackberry puree.

4. Combine Mixtures: Gradually add the wet ingredients to the dry ingredients, stirring until smooth.

5. Add Boiling Water: Carefully stir in the boiling water until the batter is well combined. The batter will be thin.

6. Divide Batter: Pour the batter evenly into the prepared cake pans.

7. Bake: Place in the preheated oven and bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.

8. Cool: Remove from the oven and allow the cakes to cool in the pans for about 20 minutes. Then transfer them to a wire rack to cool completely.

9. Prepare Frosting: In a large bowl, beat the unsalted butter until creamy. Gradually add powdered sugar and blackberry puree, mixing until smooth and fluffy.

10. Assemble the Cake: Once the cakes are completely cool, place one layer on a serving platter. Spread a generous amount of frosting on top, then place the second layer on top.

11. Frost the Cake: Frost the top and sides of the cake with the remaining blackberry frosting.

12. Garnish: Decorate the top with fresh blackberries for an elegant touch.