Step 1

Make the Chocolate Mousse: In a medium saucepan, whisk together 1+1/2 cups heavy cream, egg yolks, and sugar and cook over medium heat for about 1-2 minutes until it coats the back of a spoon. Do not boil at any time. Remove from heat and continue whisking about 1 minute. Add melted chocolate and whisk consistently. Transfer to a bowl and let cool completely. If your chocolate ganache breaks, then read the blog post above to know how to fix the ganache easily.

Step 2

Preheat oven to 350°F/175°C. Line the bottom and the sides of a 9" / 23cm baking pan with parchment paper. Set aside.

Step 3

Make the chocolate cake layer: In a medium bowl combine flour, cocoa, sugar, baking powder, and salt and stir to combine. Set aside. In a large mixing bowl with a stand or handheld mixer fitted with a whisk or paddle attachment, beat oil, egg, buttermilk, and vanilla* just until combined. Stir in dry ingredients to combine. Slowly mix in hot cocoa until combined. The batter will be thin. Transfer batter to the prepared baking pan. Bake for 16-18 minutes or until a toothpick in the center comes out clean. Don't overbake. I baked mine for 18 minutes. Let cool in the pan for about 20 minutes. Then open the springform pan and let cool to room temperature.

Step 4

Continue with the Chocolate Mousse: With a handheld or stand mixer fitted with a whisk attachment, whisk 1+1/2 cups heavy cream until soft peaks form. Add powdered sugar and whisk until stiff peaks form. Stir about 1/4 of whipped cream into the cooled chocolate cream with a whisk. Then gently fold in the remaining whipped cream with a wooden spoon.

Step 5

Assemble the cake: Cut a thin layer off the top of your cake to create a flat surface. Close the springform pan again. Spread the chocolate mousse evenly on top of the cake layer. Chill overnight in an airtight container in the fridge.

Step 6

Make the chocolate glaze: Place chopped chocolate in a large heatproof bowl. Place heavy cream in another heatproof bowl and microwave until very hot, almost boiling for about 1-2 minutes. Pour over chocolate and let stand 1-2 minutes. Whisk until smooth, and the chocolate is completely melted. Let cool in the fridge for about 10-15 minutes that it thickens. Test the consistency of the glaze down the side of the bowl. It should drip. The longer it stands, the thicker it gets. If it is too firm, re-warm it a few seconds in the microwave. Once it reached the desired consistency, it's ready to spoon on top of the cake.

Step 7

Remove cake from the fridge and spoon the glaze little by little around the sides and let drip off the sides. Do this with a small spoon and do one drip at the time. Then spoon or pour the rest of the glaze on top of the cake (maybe you don't need all) and level with an offset spatula. Place cake in the fridge for 15 minutes that the glaze gets firm if needed. Decorate with grated chocolate and berries if desired or to your preference. Store leftovers in an airtight container in the fridge up to 3 days.