First, bake the sponge cake. If you are making it to be 18 cm in diameter when the cake is done, use a 15 cm in diameter cake pan. If you want to make it to be 15 cm in diameter when it is done, use a 12 cm in diameter cake pan to bake the sponge.
Pour the sponge cake dough into the 15 cm in diameter cake pan. Bake in 160°C oven for 20 minutes. This is just a guide, so use a bamboo skewer, stick it through the sponge cake and if it comes out clean, then it is ready. Let it cool. When the sponge cake has cooled down, slice into 2 halves about 1.5 cm thick. You can freeze the remaining sponge.
Bake the biscuits. Add one pinch of salt to the whisked egg white and beat with a whisk until it becomes white. Add granulated sugar in 2 to 3 portions and whip up a stiff meringue. If the meringue is soft, you won't be able to squeeze it out later, so whip it up stiffly.
Add egg yolk to the meringue in one go and mix with a whisk. Then add well sifted cake flour. Mix as if scooping the mixture up from the bottom of the bowl using a spatula. Mix until the flour disappears.
Pour the mixture in a pastry bag with a 1.3 cm round tip.
Squeeze out the mixture in lines that are 2 cm wide and 6cm long to place on the sides of the cake. Put powdered sugar in a tea strainer and sprinkle it on evenly. When the powdered sugar disappears after a while, sprinkle a lot on once again.
If you stick the biscuit mixture too close to one another, they will be flat when baked! So, leave 2 to 3mm space between each one, then they will have a nice shape when baked.
Bake in a 180°C oven for 12 to 15 minutes. I think you can bake about 3 rows at one time, so stick the ends together in the cake pan when using it for the sides.
Prepare a 18cm in diameter. If you are making it to be 15 cm in diameter at the end, then use 15 cm in diameter, loose bottom cake pan. If you don't have a loose bottom cake pan, place a paper on the bottom in a cross. Then place a thick paper on the paper so that you can pull it out afterwords. First, place the biscuit for the sides in the cake pan tightly. Then put one sponge cake on the bottom.
The cheese mousse is easy. Add sugar to the egg white and make a meringue in advance. Whip up heavy cream in another bowl until stiff peaks forms. Knead room temperature cream cheese well using a rubber spatula. Soften gelatin with 1 tablespoon of water.
Add sugar to the cream cheese and mix with a whisk. When they are mixed well, add egg yolk too and mix. Add gelatin melted over a water bath too and mix. Mix heavy cream and meringue together gently using a rubber spatula to maintain the airy texture.
Pour half of the cheese mousse mixture into the cake pan lined with biscuit.
Place the other sponge cake onto the cheese mousse.
Pour the rest of the cheese mousse mixture into the cake pan and let it chill in the refrigerator for 1 to 2 hours to harden. When the mousse has hardened, decorate with whipped cream and fruits, and then it is ready. It will have a glossy and beautiful look if you have nappage pastry glaze.
The amount for the biscuit is a little more than enough. When it is baked, use the ones which are baked nicely. You can eat the remaining biscuit just as it is or even freeze it.