• Preheat the oven to 350°F. Grease and line 3 6-inch cake pans with parchment paper. Set them aside.
• Place the chocolate chips, milk, and sour cream in a heat-proof bowl. Sift the cocoa powder into the bowl and set it aside.
  56g (2oz) semi-sweet chocolate chips, ½ cup milk, ¼ cup sour cream, ½ cup black cocoa powder **
• Place a small saucepan fill with 3-inches of water over high heat. Bring the water to a boil and reduce it to a simmer. Place the heat-proof bowl over the mouth of the pot and stir until the chocolate melts and all the ingredients are thoroughly integrated. Take the mixture off of the heat and set it aside to cool.
• While the chocolate is cooling, sift the flour, baking powder, and soda into a medium-sized bowl. Add the salt and whisk to combine. Set it aside.
  2 cups cake flour, 1 tsp baking powder, 1 tsp baking soda, 1 tsp kosher salt
• In the bowl of a stand mixer fitted with a paddle attachment place the butter and sugar. **** Cream the sugar into the butter until light and fluffy. Add the eggs to the mixture one at a time, scraping down the sides of the bowl as needed. Add the vanilla and mix until fully integrated.
  1 cup unsalted butter, 1⅓ cup granulated sugar, 4 large eggs, 2 tsp vanilla extract
• Pour the chocolate mixture into the egg mixture and mix until uniform. Add half of the flour mixture and mix until no streaks remain. Repeat with the remaining flour mixture.
• Fill the prepared pans with the cake batter. Add roughly 400g of batter to each pan. Smooth tops with an offset spatula and transfer the cake to the oven. Bake for 50 minutes, rotating the pans once halfway through.
• Take the cakes out of the oven and remove them from their pans. Place the cakes on a cooling rack and set them aside to cool for two hours.

For the Ganache

• While the cakes are cooling, make the ganache. Place the chocolate, cream, and honey in a heat-proof bowl. Sift in the black cocoa powder and set it aside.
  200g (7oz) semi-sweet chocolate chips, ½ cup heavy cream, 2 tbsp honey, 2 tbsp black cocoa powder
• Once again, bring a small saucepan filled with 2-3 inches of water up to a boil before reducing it to a simmer. Place the heat-proof bowl over the mouth of the pot and stir until the chocolate melts and all the ingredients are thoroughly integrated.
• Take the chocolate mixture off of the heat and whisk in the sour cream. Transfer the ganache to the fridge and chill for 15-20 minutes before frosting.
  ⅓ cup sour cream

To Assemble

• Level the cakes and place one layer, cut side up on a turntable. Spread a little ganache on top of the layer and place a second cake layer on top. Repeat.
• Once the third cake layer is in place, coat the cake evenly with the remaining ganache. Cover the cake with the blackberries and dust the berries with luster, if using. Chill the cake for an hour prior to serving.
  1.1 kg (2.5 lbs) fresh blackberries ***, iridescent luster dust