Preheat your oven to 350°F (175°C) and prepare two 8-inch round pans by greasing and dusting with flour.

Whisk together the all-purpose flour, black cocoa powder, cocoa powder, baking powder, baking soda, and salt in a large bowl.

Cream the softened unsalted butter and granulated sugar on medium speed until light and fluffy, then add eggs and vanilla until combined.

In a separate cup, mix the blackberry puree, buttermilk, and coconut oil until well combined.

Gradually add the dry ingredients to the butter mixture, alternating with the blackberry mixture, mixing until just combined.

Divide the batter evenly between the prepared pans and bake for 25–30 minutes or until a toothpick comes out clean.

Cool the cakes in the pans for 10 minutes, then transfer to a wire rack to cool completely.

Combine blackberries, sugar, lemon juice, and a cinnamon stick in a saucepan and cook until softened, then stir in a cornstarch slurry.

Heat cream until steaming, then pour over chopped chocolate. Let sit, then stir until smooth, adding butter for glossiness if desired.

Assemble the cake with layers of blackberry filling and ganache between the cakes and pour remaining ganache on top.

Garnish with fresh berries and serve once ganache has set at room temperature.