Chocolate Sponge Cake

1. In a bowl, add eggs and sugar, then use a hand mixer on high speed to initially whip the mixture. Once it starts to increase in volume, switch to low speed to create fine bubbles.
2. Continue mixing until the whole mixture turns pale and fluffy. Lift the batter and draw a figure-eight pattern; when the letters slowly disappear, that's the perfect consistency for whipping.
3. Sift in the cake flour and cocoa powder. Use a rubber spatula to gently scoop up the mixture from the bottom and rotate it to combine, making sure to mix it lightly and evenly.
4. While transferring vegetable oil to the rubber spatula, pour it all over the batter and quickly mix it in. Pour the mixture into a baking pan lined with parchment paper and bake in a preheated oven at 175°C (345°F) for about 15 minutes.
5. Once the cake has cooled, remove it from the mold and cut it into a size slightly smaller than the mold for the mousse.
6. Place the sponge cake in the center of the bottom of the mold and refrigerate it until the mousse is ready.

Chocolate Mousse

1. Combine 50ml of chocolate and heavy cream and melt them together in the microwave or using a double boiler. If using the microwave, take it out a few times and stir the mixture each time. If using a double boiler, also stir the mixture while melting it.
2. Whisk the remaining 200ml of heavy cream until it forms soft peaks.
3. Adjust the melted chocolate to around 45°C (113°F) and add a portion of the whipped cream to it, then mix with a whisk. Incorporate the remaining whipped cream using a rubber spatula to combine.
4. Pour the sponge cake into the bottom-lined mold, flatten the surface, and chill in the freezer for at least 2 hours.

Chocolate Mirror Glaze

1. Soak plenty of sheet gelatin in cold water to soften it. If using powdered gelatin, sprinkle 4 tablespoons (60ml) of water over it to bloom.
2. In a small saucepan, combine granulated sugar, cocoa powder, water, and heavy cream. Heat over low heat while stirring to prevent the bottom from burning, until the granulated sugar is dissolved.
3. Turn off the heat and add the softened gelatin, squeezing out any excess water, then mix until dissolved. If using powdered gelatin, add it along with the water it was soaked in, and mix until fully dissolved.
4. Strain the mixture through a strainer and transfer it into a container that makes it easy to pour onto the cake. Let it sit at room temperature until it reaches around 30°C (86°F) to adjust the temperature.
5. Remove the cake from the freezer and carefully remove it from the mold, using a warmed towel around the sides of the mold if necessary. Place the cake on a cake cooler with a tray underneath.
6. Pour the glaze over the cake in a circular motion, starting from the center and working outward. Pay special attention to the sides of the cake, as they can be more challenging to coat with the glaze. Repeat the process several times, moving back and forth, to ensure thorough coverage.
7. Once the glazing is complete, quickly transfer the cake to a plate before it sets. To move the cake without damaging the glaze, you can use two long palette knives or knives crossed underneath the cake and gently transfer it to the plate.
8. After transferring the cake to the plate, let the mousse thaw in the refrigerator for about 1 hour.

Decoration

1. Add gold powder and gold leaf as decorations, and it's ready to serve! Use a warmed knife to cut and enjoy!