DAY 1:

Making the Cake Layers:

Preheat the Oven:

• Preheat your oven to 180°C (350°F). Grease and line two 8-inch cake tins.

Prepare the Batter:

• In a large bowl, whisk together the cocoa powder, coffee, and hot water.
• Add the vegetable oil, buttermilk, and eggs to the mixture and whisk until combined.
• Stir in the flour and both sugars until the batter is smooth.

Activate the Baking Soda:

• In a separate small bowl, add the baking soda and pour the vinegar over it. This will start bubbling. Stir quickly and add it to the batter, whisking gently.

Bake the Cake:

• Pour the batter evenly into the prepared cake tins.
• Bake for 35-40 minutes, or until a toothpick inserted into the center comes out clean.
• Allow the cakes to cool completely once baked.

Making the Chocolate Mousse:

Prepare the Tin:

• Line the sides of a tall loose-bottomed or springform cake tin with baking paper or acetate.

Whip the Cream:

• In a large bowl, whip the double cream on high speed until firm peaks form. Refrigerate until ready to use.

Whip the Egg Whites:

• In a separate bowl, whisk the egg whites until foamy. Gradually add the granulated sugar while continuing to whip.
• Whip until stiff peaks form. Refrigerate until ready.

Melt the Chocolate:

• Place the dark and milk chocolate in a microwave-safe bowl and heat in 15-second intervals, stirring each time, until melted.
• Stir in the egg yolks and salt. The mixture will become thick, which is normal.

Combine Ingredients:

• Add a large dollop of the whipped cream into the chocolate mixture to loosen it up. Then gently fold in the remaining whipped cream.
• Fold in half of the whipped egg whites, then the remaining egg whites, ensuring there are no lumps.

Assembling the Cake:

Prepare the Cake Layers:

• Once the cake layers have cooled, trim the tops to create flat, even layers.

Layer the Cake:

• Place one cake layer into the prepared tin.
• Spread half of the chocolate mousse evenly on top of the cake.
• Place the tin in the freezer to chill for 20 minutes.

Making the White Chocolate Mousse:

Whip the Cream and Egg Whites:

• Follow the same process as with the chocolate mousse. Whip the double cream and egg whites until stiff peaks form.

Melt the White Chocolate:

• Melt the white chocolate in the microwave as you did with the dark chocolate.
• Stir in the egg yolks and salt, followed by the vanilla bean paste (or extract).

Combine Ingredients:

• Gently fold the whipped cream and egg whites into the white chocolate mixture to form the mousse.

Layer the Mousse:

• After the chocolate mousse has chilled for 20 minutes, remove it from the freezer and add the white chocolate mousse on top of it.
• Add the final layer of cake on top.
• Place the entire cake in the fridge to set overnight.

DAY 2:

Remove and Serve:

• The next day, remove the cake from the tin.
• Slice and enjoy your delicious multi-layer mousse cake!