In a bowl, mix all ingredients except for the oil, and beat the ingredients using a hand mixer.
Mix for about 2 minutes until it lighten and becomes a bit whiter, then add in the oil and beat for about 30 seconds.
Pour it into a 5� x 5� x 3� cake pan.
Bake at 170�C for 20 minutes.
Once the cake has done, let it cool down on the wire rack.
Then, prepare the same cake pan and place the chocolate sponge cake at the bottom.
Step 2: Dark Chocolate Mousse
Add water into your gelatin, still and let it bloom for about 10 mins.
Simmer the milk and sugar in a pan using medium heat.
Once it has started to simmer, turn off the heat, add in the bloomed gelatine and stir until it melts.
Pour the mixture into a bowl of dark chocolate, and quickly stir it using the hand whisk until all the chocolate melts and there are no chunks left. Set aside.
In another bowl, beat the whipping cream until it creates firm peaks.
Slowly fold in the cream and chocolate mixture together until it is well combined.
Pour the dark chocolate mousse mixture into the cake pan with the sponge cake at the bottom, and let it set in the freezer for 15 minutes.
Step 3: Milk Chocolate Mousse
Similar to the dark chocolate mousse, repeat the same steps (from number 1 - number 6).
Slowly pour the milk chocolate mousse mixture on top of the dark chocolate mousse layer and let it set in the freezer for 15 minutes.
Step 4: White Chocolate Mousse
Similar to dark and milk chocolate mousse, repeat the same steps (from number 1 - number 6).
Then slowly pour the white chocolate mousse mixture on top of the milk chocolate mousse layer and let it set in the freezer for 8 hours or more, until the whole cake has fully set.
After 8 hours, you can take out your cake, and it�s ready to serve!