This cake is absolutely decadent with hints of coffee combined with a filling and topping of roasted blueberries and blackberries. This chocolate cake is masculine and feminine all in one amazing bite.
Place blueberries and blackberries in a baking dish and toss with sugar and vanilla bean and seeds.
Roast for 20 minutes. Cool to room temperature before filling or topping cake.
Preheat the oven to 350 degrees F.
Spray two 8-inch x 2-inch round cake pans with non-stick cooking spray. Line with parchment paper, then lightly spray parchment and flour the pans.
Sift the flour, sugar, cocoa, baking soda, baking powder, and salt into the bowl of an electric mixer fitted with a paddle attachment and mix on low speed until combined.
In another bowl, combine the buttermilk, oil, eggs, and vanilla. With the mixer on low speed, slowly add the wet ingredients to the dry. With mixer still on low, add the coffee and stir just to combine, scraping the bottom of the bowl with a rubber spatula. Pour the batter into the prepared pans and bake for 35 to 40 minutes, until a cake tester comes out clean.
Cool in the pans for 30 minutes, then turn them out onto a cooling rack and cool completely.
Place 1 layer, flat side up, on a flat plate or cake pedestal. With a knife or offset spatula, add a thin layer of roasted berries and reserve the remainder for topping.
Place the second layer on top, rounded side up, and spread the frosting evenly on the top and sides of the cake.
Add a rustic mound of roasted berries on top.
Chop the chocolate and place it in a heat-proof bowl set over a pan of simmering water. Stir until just melted and set aside until cooled to room temperature.
In the bowl of an electric mixer fitted with a paddle attachment, beat the butter on medium-high speed until light yellow and fluffy, about 3 minutes. Add the egg yolk and vanilla and continue beating for 3 minutes. Turn the mixer to low, gradually add the confectioners' sugar, then beat at medium speed, scraping down the bowl as necessary, until smooth and creamy. Dissolve the coffee powder in 2 teaspoons of the hottest tap water. On low speed, add the chocolate and coffee to the butter mixture and mix until blended. Don't whip! Spread immediately on the cooled cake.