Chocolate mousse cake

Chocolate. Mascarpone. More chocolate. Heavy cream. Sugar. Nine eggs. Nearly no flour. 
Do you think it will be a good cake? 
It is not enough to say it is good, it is the best chocolate cake with two fudgy layers and smooth chocolate mousse between them. And, of course, the mascarpone which fills the mouth with heaven. 
I have always wondered what is the meaning of the word "decadent" concerning cake, but this chocolate cake is decadent, I am sure. It includes so many costly and tasty ingredients, that the occasion you prepare it for should be worth the money and all the efforts. 
Or you should love a lot the people you prepare it for. 
I love my sister Eve. A lot. 
She has a warm heart and is cheerful and always in good faith. She is a psychologist - a really good one and I am very proud of her. 
Some months ago I needed advice. I was so involved into the situation, that I really didn't know what to do. She was the one who showed me the right way to get out of the situation and it was a really, really important decision with lots of important consequences. 
Thank you, Eve, I will never forget your advice! 
So I wish to express my gratitude and love to her and I know how - I will prepare her favourite cake. 

It is not enough to say Eve loves chocolate, because she is one of the most devoted chocoholics I know. This one will be for her, but here is the recipe if you want to please somebody you love.  

Ingredients
For the fudge cake (10-inch springform pan):

• 8 oz (225 g dark chocolate)
• 1 cup (200 g) butter
• 1 cup (130 g) sugar
• 5 large eggs
• 1/4 cup (32 g) flour
• 1/4 teaspoon salt
• 1 Tbsp vanilla

For the chocolate mousse:

• 8 oz (225 g) dark chocolate
• 1/2 cup (100 g) butter
• 4 large eggs at room temperature, divided
• 1/4 cup whipping cream
• a pinch of cornstarch
• 1 Tbsp vanilla
• 1/2 cup sugar

For the mascarpone layer:

• 18 oz (500 g) mascarpone
• 1 cup (250 g) heavy cream 
• ½ cup sugar
• 2 packets vanilla powder

Preparation:

Fudge Cake Layer. Preheat oven to 325 F (160 C). Butter 10-inch springform pan and dust with powder sugar. Melt chocolate and butter over low heat, stirring constantly. Set aside to cool for 10 minutes and add sugar. Add eggs one at a time and stir well to incorporate after each egg addition. Mix in vanilla, salt and flour, stir again to get an uniform texture and pour batter into the pan. Put into the oven for 30-40 minutes until cake rises into the center. Let cool on a rack for at least an hour (center will fall). 
Loosen the cake from the pan and divide into two slices horizontally.

Chocolate mousse. Put egg yolks, whipping cream and vanilla in a bowl and whisk to blend.

Cut butter into pieces. Put butter into a metal bowl over a pan with simmering water but make sure the bottom of the bowl does not touch the water.  Gradually add the egg mixture to the melted butter stirring constantly for about 5-6 minutes (the mixture will get thick and custard-like). Remove bowl from the simmering water. Chop chocolate very finely and add to the hot mixture. Stir until melted.

Beat egg whites with the sugar and the cornstarch until medium-stiff peaks appear. Add stepwise the beaten egg whites to the warm chocolate.

Put chocolate mousse into the fridge for some hours to set.

(It would be best if you prepare the cake and the chocolate mousse the day before arranging the cake).

Mascarpone Layer. Whisk cream until fluffy and start adding the sugar without stopping the mixer until well blended. Stir in mascarpone and vanilla, mix for additional minute or two and set aside. Put into the fridge for an hour or more to set.

Arrange the cake. Put one of the cake layers onto a large flat plate. Pour mousse over the layer and distribute evenly with a spatula. Put the other layer above. Spread mascarpone layer above. You could also cover the sides if you prefer a better look of the cake). Chill.

Like most cakes, this one tastes better the day after arranged when all the tastes are blended.