Blackberry Velvet Gothic Cake - Dramatic Chocolate Dessert

Ingredients

• 2 cups all-purpose flour, sifted
• 1 1/2 cups granulated sugar
• 1/2 cup black cocoa powder (you can find this online or at specialty baking stores)
• 1/2 cup regular cocoa powder
• 1 cup unsalted butter, softened to room temperature
• 3 large eggs, at room temperature
• 2 teaspoons pure vanilla extract
• 1/4 cup coconut oil or olive oil
• 2 teaspoons baking powder
• 1 teaspoon baking soda
• 1/4 teaspoon salt
• 1/4 cup fresh blackberry puree (about 1 cup berries blended and strained)
• 1 cup buttermilk, at room temperature
• A few drops purple or red food coloring (optional, for a more dramatic color)
• 2 cups fresh or frozen blackberries
• 1/4 cup granulated sugar
• 1 tablespoon fresh lemon juice
• 1 tablespoon cornstarch
• 1 cinnamon stick
• 2 tablespoons water
• 1 cup heavy cream
• 1 1/2 cups semi-sweet or dark chocolate, finely chopped (good quality chips work too)
• 1 tablespoon unsalted butter (optional, for extra shine)
• Fresh blackberries
• Chocolate decorations like skulls or other spooky elements
• Edible gold dust or black sprinkles