Preheat the oven to 350ºF (177ºC) and prepare a 9-inch springform pan by spraying the sides with cooking spray and fitting the bottom with a parchment circle. I also like to line the outside of the pan with aluminum foil to ensure there is no leakage of cake batter, but if you're sure your springform pan is leak-proof you can skip the aluminum foil.

Place all of the dry ingredients into a large bowl and whisk to combine. Add the vegetable oil, eggs, vanilla, and buttermilk and whisk until uniform. Add the hot coffee (or hot water) in a slow stream, then whisk until smooth and combined. The batter will be very thin.

Pour into the prepared cake pan and bake for 25-30 minutes, until a toothpick inserted comes out clean. Cool completely before moving on to making the chocolate mousse.

Place the semi-sweet chocolate chips into a large glass or metal bowl and set aside.

Place 1 Cup (240ml) of the heavy whipping cream into a small saucepan set over medium-low heat. Whisk frequently until the cream begins to simmer around the edges, then pour it over the chocolate chips and whisk until it becomes a smooth ganache. Set aside until the ganache cools to room temperature, about 25 minutes. Wait until it is room temperature to move on to the next step.

In the bowl of your stand mixer fitted with the whisk attachment (or using a medium bowl and hand mixer), add the remaining 1 ⅓ Cups (320ml) of heavy whipping cream, powdered sugar, vanilla, and instant coffee or espresso powder (if using). Mix at low speed until the ingredients are combined, then turn the mixer to high and beat until stiff peaks form, about 4 minutes.

Add the whipped cream mixture to the cooled ganache and fold gently with a rubber spatula until there are no streaks.

Remove the cooled chocolate cake layer from the springform pan. Using a serrated knife or cake leveler, level the top of the cake to create an even layer. Gently peel off the parchment paper on the bottom of the cake layer, then place it back into the springform pan.

Wrap an acetate cake collar around the cake layer and secure it with a piece of scotch tape. This will help keep the mousse in place as it sets.

Add the chocolate mousse on top of the cake layer and smooth it down with an angled spatula until it reaches the edges of the acetate and has an even surface. Refrigerate for 6 hours, or overnight.

Wait until the chocolate mousse cake is set before making the chocolate ganache unless you're making it ahead of time (instructions for making ahead and reheating are in the notes section of this recipe).

Place ½ Cup (93g) of semi-sweet chocolate chips into a medium glass or metal bowl and set aside.

Add ½ Cup (120ml) of heavy whipping cream into a small saucepan set over medium heat. Bring to a simmer, whisking frequently, then pour it over the bowl of chocolate and whisk until uniform and smooth. Allow the chocolate ganache to cool to room temperature, about 20 minutes.

Once the mousse cake is set, unclip the springform collar and remove it. Then, unwrap the acetate from the sides of the mousse cake.

Pour the cooled chocolate ganache over the top of the cold chocolate mousse cake and spread it with an angled spatula until it runs over the edges. To create the look pictured, garnish with fresh raspberries and chocolate covered espresso beans in a crescent design. Serve immediately, or place back into the refrigerator until you're ready to serve.