Preheat the oven to 175°C (350°F) and grease and line 2 round cake pans.

Sift the all-purpose flour, cocoa powder, baking powder, baking soda, and salt into a mixing bowl.

Beat 125 g unsalted butter, 90 ml olive oil, and 350 g granulated sugar until pale and creamy.

Scrape in the seeds from 2 vanilla beans and beat them into the butter mixture.

Add the 4 eggs one at a time, beating well after each addition.

Add the sifted dry ingredients and 170 ml whole milk alternately, mixing only until combined.

Stir 60 ml boiling water into the batter until it becomes smooth and pourable.

Divide the chocolate batter evenly between the prepared cake pans.

Bake the cake layers for about 30 min, until a skewer inserted in the centre comes out clean.

Cool the cake layers in their pans for 10 min, then transfer them to a wire rack.

Combine 125 ml water and 110 g granulated sugar in a saucepan and bring to a boil.

Simmer the syrup for 3 min, then remove it from the heat.

Stir 60 ml cognac into the warm syrup and let it cool completely.

Cook 450 g frozen forest fruits and 110 g granulated sugar in a saucepan over medium heat until the fruit releases juices.

Mix 2 tsp cornstarch with 2 tbsp water until smooth, then stir the slurry into the fruit mixture.

Simmer the forest fruit filling for 2 min until thickened, then cool it completely.

Beat 250 g mascarpone with the seeds from 1 vanilla bean until smooth.

Whip 1 litre heavy cream and 200 g powdered sugar to medium-stiff peaks.

Fold the whipped cream into the mascarpone mixture until the frosting is smooth and stable.

Place one cooled cake layer on a cake stand and brush it with half of the cognac syrup.

Spread a layer of mascarpone frosting over the cake, then spoon over half of the forest fruit filling.

Set the second cake layer on top and brush it with the remaining cognac syrup.

Cover the cake with the remaining mascarpone frosting and smooth the surface.

Decorate the cake with the remaining forest fruit filling and red berries.

Refrigerate the finished cake for at least 120 min before slicing and serving.